Hey everyone, sorry that you are reading another one of these kinds of posts but I just wanted to fish for some feedback on a situation my group has in one of our campaigns (we are currently running 2 campaigns with 2 different DMs who are also players in each other's game, and I am set to DM a 3rd campaign as one of the prior two is close to it's end).

We are having some issues with one of our players feeling like they are being overridden by the rest of the party but the discourse isn't progressing at all or if it does it isn't in a healthy way. I'll mock up a TLDR at the bottom after I get all of my thoughts and context written out. I'll begin with a list of the players identified by their classes, the alignments of the characters, and a snip of the people playing them:

1) Fey Ranger: (CG) This is me. 16 year veteran player, started in highschool. Played 3.5, Pathfinder, Anima, and of course 5e. I've DMed 5e a handful of times.
2) Paladin: (LG) 16 year veteran player, part of my core group from HS. Played and DMed 3.5, prefers 3.5 over 5e. One of two currently running DMs, subject of my post.
3) Bard: (N) 16 year veteran player, part of my core group from HS. Hosts our games, has not been DM.
4) DM: Veteran player, uncertain of experience but he clearly knows his stuff; between Forgotten Realms lore and gameplay rules to the point of being aware of errata changes I feel pretty confident taking his word at face-value. The second of two current DMs, but will be called DM for the sake of the post.
5) Druid: (CN) Has been playing for about 5 years, but does not have much group experience outside of our own. Shows almost all of the creative hallmarks of a newer player: chaotic characters who tend to be the same personality with different abilities, not much lore knowledge, more of a "along for the ride unless I can do something funny" kindof playstyle. (Nothing wrong with it at all, I love the guy and regularly try to engage him in roleplay to help him think "in character" more).
6) Cleric: (NG, later NE) Started playing within the past two years, is Bard's actual wife. Very good new player characteristics - accepts plot hooks ambitiously, has a long-term plan for her character, actively tries to seek out roleplay. Very much a "Yes, and" type of player who just needs to nail down gameplay basics and rules.

In our DM's game, Cleric had accepted a bargain from Asmodeus to become one of his followers and do his bidding in exchange for occasional rewards early in the story, only known by a few party members at first and slowly becomes an open secret within the party. The game was not painted to be an evil-themed campaign in session zero, but because of how receptive Cleric is, the DM will often feed off of the energy she brings and provide adventure hooks via this vehicle to advance the plot. Essentially we know that she worships Asmodeus, we just don't talk about it and to varying degrees try to protect her from being discovered.

Some events in our world have caused the Holy Army to assemble and prepare to invade a city whose ruling family is made up of vampires. Contained inside the city is this McGuffin that is being guarded by the vampiric family because they believe that if it falls into the wrong hands it could mean the literal end of all reality. Basically the vampiric family is being used as a scapegoat by the actual bad guys so the Holy Army wipes them out, leaving the McGuffin defenseless. In any case, the Party knows that the vampires are not to blame for the events that kicked off the crusade and we feel a sense of urgency to stop it. Paladin isn't keen on working with the vampires because they are innately evil in the lore of Forgotten Realms (our overarching setting), and often times refuses to participate in corresponding with the vampiric family. 

Asmodeus pops up again and tells Cleric that he wants to collect the souls of the Leader of the Holy City and the Marshal of the Holy Army. In return, he will provide aid to her and anybody else who helps her in carrying out an assassination plot against them... provided they knowingly agree to the plot prior to it's execution. Cleric agrees to the plot seeing it as a way we could stop the holy army and pitches it to the party;

Bard sees that it is an evil offer but believes that evil in the name of the greater good is acceptable. 
Druid does not feel right about doing the killing because the leader and the marshal haven't ever done anything to hurt him, but wants to try and convince them to call off the invasion so agrees to go along.
Ranger isn't part of the party proper yet, he is currently acting as an "unseen fey guardian", so he follows the party from afar and intervenes when they need a hand.
Paladin hates everything about this but agrees with Druid that perhaps they can be reasoned with.

The assassination is a partial success; the party goes to the holy war camp, fenagle their way into a meeting with all they key people, and gets set up in a room with just the Marshal, the Leader, and the Leader's Assistant present. The Leader turns out to be corrupted by his assistant which ticks off Paladin... who actually ends up attacking the Leader first and begins combat. Bard and Cleric successfully kill the marshal, but Paladin and Druid kill the leader to save his soul from being harvested (some meta-game stuff happened here, don't get hung up on this lol). After this encounter, Ranger formally presents himself to the party and offers to help them escape the camp.

Paladin becomes depressed and starts closing off from the party, doesn't talk to anybody about what is going on or how ask how we feel about the situation when we stop to camp or rest. Ranger tries to engage with Paladin who literally does not reply to him and trudges on silently.

Because of the partial success Asmodeus is pretty upset with Cleric, but because she's pretty good at being his follower, Asmodeus offers her a new deal and a chance to redeem herself. Her three choices are:
1) She finds a way to summon and kill an angel to harvest it's wings to be used in a ritual that would effectively destroy the Holy Army. This option makes the party 100% even-steven with Asmodeus.
2) Asmodeus kills her, takes her soul, doesn't lift a finger to help anything at all, and instead sends his other followers out to hunt the rest of us down and sacrifice us. 
3) She kills Paladin and Druid for interfering with the original contract, which basically only saves her and we still have the invasion to deal with.

She mulls it over with the party and chooses option 1 and we figure out a way to get the job done. Paladin is the only one who disagrees with the plan, understandable.

Paladin's player cant make the session where we do the summoning and killing, which is fine by him because he says his character would not help with the plan at all. Instead, Paladin is assumed to be guarding the room that contains the McGuffin.

Everything works out the way it was sold to us; we saved the citizens and safeguarded the reality-ending McGuffin in exchange for damning about 70% of the Holy Army and killing a planetar angel. Everyone in the party had motives for agreeing to the plot:

Bard recognizes the chance for diplomacy with the paladins has passed following the assassination of the leaders of the Holy City and the Holy Army is just about on the gates of the city. Pressed for time, he doesn't see any other way to stop the army.
Druid is along for the ride, but now has the sentiment that the paladins were "mean to him" when the party was at their war camp, so he doesn't care what happens to them.
Ranger has a self-driven conviction to protect the party which he views as a surrogate family and decides that killing an angel is better than letting Asmodeus take any of them away.

SO NOW WE FINALLY CAN GET TO THE POINT OF MY POST. Sorry, I tried to cut it as dry as I could leading up to here.

I spoke with Paladin after the last session wrapped up because he asked how everything went. After telling him what happened, he said me that he is planning on dropping out of the game entirely. He claims that the character he made doesn't fit the party, that we are all evil characters and he doesn't understand why the party can't or won't consider doing good things, that the things we have done are some of the most evil things you can do and that we don't realize that. He also has no doubt in his head that our characters are completely evil regardless of what we think, that he is constantly being overridden when we make group decisions, and he refuses to try to find ways to resolve the actions of the party in a way that allows his character to participate in the adventure. He says because PvP isn't an option, the only way he sees being able to change the party's mind is sabotaging our plans and hoping that DM will eventually provide consequences for our actions... and has even called us murderhobos.

This is a bit melodramatic right? I mean half of the players are veteran players; the party as a whole is just accepting the plot hooks that the DM provides, and we are working our asses off to figure out how our characters come to terms with the things they have done. To me it feels like he isn't putting in work to have his character be a three-dimensional member of the party and is really just upset that we aren't playing our characters the way he wants us to play them. I get that disagreements happen within parties, and that maybe we as players could have looked harder for other solutions, but ultimately we have to play as a group. You're not always gonna get everyone onboard with you 100%, and you can't just sit and pout as a character and fall back on the "that's what my character would do" argument when the actions of the party don't line up perfectly with your sentiment of character alignment. The Cleric accepts that she is evil and as a player has even said that she hopes that eventually there's a point in the game where she can be "redeemed" and turn away from Asmodeus, but the rest of us didn't design evil characters and none of us are doing these evil things with the intent of spiting good; we are trying to protect existence as we know it. It's not like Paladin or his player would know that though because the player chose to make the character disengage from us completely and be distant; roleplay just doesnt happen anymore. 

Let me know your thoughts, and maybe some things I should think about when I take up the mantle of DM. Our group is a private group, we aren't playing at game stores so it's not like we are gonna just replace this player with someone else. He's already drafting characters for my campaign.

With the caveat being that we are only getting your side of the story and there might be things we are missing, here is my thought:

The reason they are “putting in work” to make a three dimensional character is they are probably not a three dimensional person.  Based on how you characterised the conversation you had with them - specially that they said that they did not understand a more morally diverse party, rather than say “my character does not understand this party” - they likely are the kind of person who sees the world in black and white and has an extremely morally simplistic view of reality they transmute into their characters.

That is not bad, per se, but it can be problematic if the rest of the group leans toward something other than the most boring possible implementation of Lawful Good.  I am sure there are people like this who can play in a more diverse group - though I have never met them - but often time these people shut down completely because accepting their character might be wrong would be tantamount to accepting their rather limited worldview might be wrong.

So, what do you do to fix these kinds of people?  Well, if you have an absolute answer to that question, you could sol d many of the world’s evils.  But that’s not a reasonable expectation for a D&D game, so let’s focus on what can be done:

1. The DM could hasten the redemption of the party - this is punishing the rest of the party for one person’s lack of moral introspection, but can provide one path to party harmony.

2. The DM could make the “good” side of “evil for the sake of good” obvious and quickly apparent - though this is again taking some of the fun from the majority of the party.

3. You could have the DM talk with the person - they have more authority than you and players are more likely to listen to the DM than the other players.

4. The Cleric could try to explain their motives in a way that appeals to the real world player (not just their character).

5. Your DM can try to change their character by putting them in situations where they might come around to your party’s way of thinking. This can be hard to do if your DM is not a manipulative person.

6. You can give it a little longer and see if it works itself out with more sessions - ideally with the players trying to go out of their way to engage the paladin in roleplay and make the paladin understand their positions. 

7. The DM can ask that player to leave - this is a nuclear option and should not be an early consideration.

It is also important that everyone understands that someone not meshing with a party does not necessarily mean there are hard feelings or that the other person is a bad player - sometimes players just do not work out together in game. 

Based on what you've described it's probably for the best that the Paladin character leaves the campaign.  A lawful good character, especially a paladin, would have a very hard time justifying the actions your party are taking.  I can imagine they may feel "betrayed?" that this is no longer what they signed up for, since you had a session 0 but have leaned hard in another direction.  

Friends can disagree while still having a discussion, so maybe see if they want to try a different character that better fits the party dynamic.  If they don't that's ok.  He's still joining your upcoming campaign.  If all sides keep a civil open dialogue, and try to understand the other side's point of view, things should work out.

This is what happens when people are too concerned with Alignment outside of character creation. Once your character is fully formed and has something of a personality, Alignment should be considered much more DEscriptive than PREscriptive. If you're too absoloutist, you can basically only function in a party with others of the same alignment.

Quote from CharlesThePlant >>

This is what happens when people are too concerned with Alignment outside of character creation. Once your character is fully formed and has something of a personality, Alignment should be considered much more DEscriptive than PREscriptive. If you're too absoloutist, you can basically only function in a party with others of the same alignment.

 While I agree with you, even if you take alignment out of the equation, having a party where one character is a "truth, justice, and the American Way" type and another is a willing servant of the setting's analogue to Satan is bound to cause friction.

Well. Your group is dysfunctional. Basically, you have this one guy who'd simply never run around doing the bidding of an archdemon - while the rest of the group are kinda fine with it. That basically cannot work out. And ... yea, since I'm that kind of guy - I never, ever play outside my real life morals in games - I kinda get it. If your guy was playing another character, not a paladin, that still wouldn't solve anything.

A long time ago, I was in a similar situation. I was the paladin, my best friend was a black robe wizard. We were able to keep the disagreements in character - albeit very loud - and that worked out and was fun and all. But ... well, we were very close, otherwise that wouldn't have worked.

It's nothing to do with alignment really.

You have a Paladin and a cleric of Asmodeus - they will never get along.

The rest of the party shouldn't really be agreeing to doing Asmodeus' work if they were characters with morals.

Just because the DM makes an offer of a plot, doesn't mean that the player has to accept that offer - especially when it is such a dubious offer as working for such an evil creature.

I suppose it doesn't help that you had a new player, and the DM took advantage of that to create this situation, since the player probably didn't realise that they could have their character refuse that offer.

Quote from CharlesThePlant >>

This is what happens when people are too concerned with Alignment outside of character creation. Once your character is fully formed and has something of a personality, Alignment should be considered much more DEscriptive than PREscriptive. If you're too absoloutist, you can basically only function in a party with others of the same alignment.

 
At no point in the thread does OP put alignment as the problem - alignment is referenced in parentheticals to provide a quick and easy description of each character (which is exactly what the system is designed for), but the OP never indicates “the Paladin says this is a problem because they are lawful good and believe they must play lawful good.”

This argument ignores how people actually think - in the overwhelming number of cases where alignment is where the problem manifests (again, no indication on the thread that is occurring here, despite your trying to blame it), those problems would manifest even if the alignment system did not exist.  You would have the exact facts described here - a person who is so stuck on their own personal morality they cannot divorce their game self and the game selves of the other players from their real selves and the real selves of the other players. 

Blaming alignment is a cop out that rarely solves the actual underlying problems - and it certainly is not helpful when (a) the OP does not put alignment at issue and (b) your post only consists of pontificating against alignment and does not bother to add any of the constructive feedback OP requested. 

Quote from Farling >>

The rest of the party shouldn't really be agreeing to doing Asmodeus' work if they were characters with morals.

Throughout history, we have seen examples of where moral individuals work with evil entities because the alternative is worse.  That is exactly what OP presented in the thread - a group of players who, for the most part, are reluctantly working with Asmodeus because he represents a stable, known evil, and the alternative is much worse—the end of everything. 

Asmodeus is, after all, pretty darn evil—but he is also a fair and stable type of evil. His domains of knowledge and order and his pertinence for keeping his contracts make him among the most trustworthy of the evil gods—you know exactly what you are getting with Asmodeus, someone who is going to scheme and plot, but who still wants the world to keep on turning in a structured manner.

Earlier editions of D&D actually made the “evil god can be a force for good” position more clear than 5e.  For example, 4e emphasised that Vecna was often worshiped by good individuals—revolutionaries who needed the good of secrets’ protection when planning to overthrow tyrants; entire good cults who used the god of secrets’ protection to protect extremely evil information from being widely disseminated.

Which all brings about a new point OP can and should raise with their played (or, probably better, have the DM and Cleric raise)—explain what aspects of Asmodeus’ Domain the party is relying on (requirement for order as opposition to chaos) and why the party is risking the more problematic aspects of Asmodeus and what the plans are to mitigate the webs Asmodeus inevitably is trying to trap them in. It probably would not hurt to point out that long-standing D&D canon has actively encouraged this kind of “deal with the devil for the greater good” play, just to remind the player that this kind of play is naked into the fabric of the game itself. 

Quote from Caerwyn_Glyndwr >>

Quote from CharlesThePlant >>

This is what happens when people are too concerned with Alignment outside of character creation. Once your character is fully formed and has something of a personality, Alignment should be considered much more DEscriptive than PREscriptive. If you're too absoloutist, you can basically only function in a party with others of the same alignment.

 
At no point in the thread does OP put alignment as the problem - alignment is referenced in parentheticals to provide a quick and easy description of each character (which is exactly what the system is designed for), but the OP never indicates “the Paladin says this is a problem because they are lawful good and believe they must play lawful good.”

This argument ignores how people actually think - in the overwhelming number of cases where alignment is where the problem manifests (again, no indication on the thread that is occurring here, despite your trying to blame it), those problems would manifest even if the alignment system did not exist.  You would have the exact facts described here - a person who is so stuck on their own personal morality they cannot divorce their game self and the game selves of the other players from their real selves and the real selves of the other players. 

Blaming alignment is a cop out that rarely solves the actual underlying problems - and it certainly is not helpful when (a) the OP does not put alignment at issue and (b) your post only consists of pontificating against alignment and does not bother to add any of the constructive feedback OP requested. 

Quote from Farling >>

The rest of the party shouldn't really be agreeing to doing Asmodeus' work if they were characters with morals.

 

Throughout history, we have seen examples of where moral individuals work with evil entities because the alternative is worse.  That is exactly what OP presented in the thread - a group of players who, for the most part, are reluctantly working with Asmodeus because he represents a stable, known evil, and the alternative is much worse—the end of everything. 

Asmodeus is, after all, pretty darn evil—but he is also a fair and stable type of evil. His domains of knowledge and order and his pertinence for keeping his contracts make him among the most trustworthy of the evil gods—you know exactly what you are getting with Asmodeus, someone who is going to scheme and plot, but who still wants the world to keep on turning in a structured manner.

Earlier editions of D&D actually made the “evil god can be a force for good” position more clear than 5e.  For example, 4e emphasised that Vecna was often worshiped by good individuals—revolutionaries who needed the good of secrets’ protection when planning to overthrow tyrants; entire good cults who used the god of secrets’ protection to protect extremely evil information from being widely disseminated.

Which all brings about a new point OP can and should raise with their played (or, probably better, have the DM and Cleric raise)—explain what aspects of Asmodeus’ Domain the party is relying on (requirement for order as opposition to chaos) and why the party is risking the more problematic aspects of Asmodeus and what the plans are to mitigate the webs Asmodeus inevitably is trying to trap them in. It probably would not hurt to point out that long-standing D&D canon has actively encouraged this kind of “deal with the devil for the greater good” play, just to remind the player that this kind of play is naked into the fabric of the game itself. 

 I only bring alignment up because I recognize the player mentality. Regardless of whether or not OP mentioned it, I've seen it enough times in player conflict to make an educated guess that the issue stems from a certain inflexibility you get when a player takes alignment prescriptively (i.e. I picked Lawful Good at the beginning of the campaign so I must Never Waver in My Conviction), rather than treating alignment as descriptive of your behavior for the most part, or descriptive of a character's ideals. 

And even if the player doesn't cite alignment by name, that black and white inflexibility is one of the common pitfalls of the way many players think about alignment-- not that I'm blaming alignment, I actually quite like alignment as a character building tool-- but many players fall into the trap of thinking of alignment as a hard rule rather than more like the Pirate's Code-- "guidelines more than actual rules." 

Sadly, the reason I don't try to supply a suggested fix is that I don't think the situation is that salvageable without drastically changing a campaign that everyone else seems happy with, and a compromise here just sounds like it would make everyone less happy. Not every player is compatible with every campaign, and a player like this should ideally be in an all-Good party, otherwise this issue isn't going to go away. The fact that the other characters have explained to the paladin that they hope to achieve good in the long run through their current actions shows deeper consideration about the character's moral standpoint, and the fact that the paladin has heard this argument and dismissed it out of turn is telling. Sometimes parting ways is just the better solution. 

Quote from CharlesThePlant >>

 I only bring alignment up because I recognize the player mentality. Regardless of whether or not OP mentioned it, I've seen it enough times in player conflict to make an educated guess that the issue stems from a certain inflexibility you get when a player takes alignment prescriptively (i.e. I picked Lawful Good at the beginning of the campaign so I must Never Waver in My Conviction), rather than treating alignment as descriptive of your behavior for the most part, or descriptive of a character's ideals. 

And even if the player doesn't cite alignment by name, that black and white inflexibility is one of the common pitfalls of the way many players think about alignment-- not that I'm blaming alignment, I actually quite like alignment as a character building tool-- but many players fall into the trap of thinking of alignment as a hard rule rather than more like the Pirate's Code-- "guidelines more than actual rules." 

Sadly, the reason I don't try to supply a suggested fix is that I don't think the situation is that salvageable without drastically changing a campaign that everyone else seems happy with, and a compromise here just sounds like it would make everyone less happy. Not every player is compatible with every campaign, and a player like this should ideally be in an all-Good party, otherwise this issue isn't going to go away. The fact that the other characters have explained to the paladin that they hope to achieve good in the long run through their current actions shows deeper consideration about the character's moral standpoint, and the fact that the paladin has heard this argument and dismissed it out of turn is telling. Sometimes parting ways is just the better solution. 

 You blame that on alignment but really, some people just don't like playing in evil campaigns because doing things like murdering an NPC just because a character's evil patron wants them to do so as part of his evil scheme isn't their idea of fun.  Especially when Session Zero outlined a game that was very different.

If I were the paladin, I'd want to leave too. Assassinating paladins and sacrificing an angelic being for the actual Devil? I get that the world is shades of grey and all that, but that action is a pretty black shade of grey. 

Brutal honesty mode: sounds like it's your DM's fault. Are they providing any avenues besides the abhorrently evil option? From your post it kinda seems like Asmodeus is the driving force that moves your plot forward, which, no matter what you think your alignment might be, will most likely make it an evil campaign. 

It doesn't seem like a melodramatic move, it seems like a pragmatic one. They'd rather not play a Good paladin going on a crusade in the name of Asmodeus. Either have the DM give you more options besides devilish deals, or have the paladin leave. (PvP isn't allowed, but the DM told the Cleric she could harvest the souls of two of the other PCs? I get that it's probably meant for shock value and not expected to be accepted,  but that sounds a lot like PvP to me).

This is all my opinion based on just reading what you wrote, though. As many have pointed out, there's probably more nuance and more facts that we don't have. At the end of the day it's your right to feel how you feel, just like it's the Paladin's right to feel how they feel. 

I don't think it is melodramatic of the Paladin player and I hope you haven't told them that they are being melodramatic. They signed up to play a particular kind of character and the current plot is pretty hostile to that character concept. I don't think I would be having fun either. Did you all have a Session 0 where you all talked about what kind of game you all wanted to play? This seems like a malfunction of the game going somewhere the player did not sign up for. It's valid for someone to want to stop playing in those circumstances and it seems like it has been going on for multiple sessions. The DM should have done some sort of check in with that player and then with the whole party in order to discuss how to shift things so everyone was having fun.

There's a stream I watch where a Paladin who worships a purple cow that can only be seen by staring into one of the suns is great friends with a warlock whose patron is the world-devouring Cthulhu who takes an active interest in the party's activities. The paladin is a low WIS LG. The Warlock is a high CHA CE. There's no friction between them.

The only occasional gameplay disruption comes from the one CG "yes and" player character who doesn't understand the "yes and I try to" method of D&D until the DM stops him and makes him roll for it before it gets on a roll. (Pun not intended, but I'll take it.)

It's not the characters. It really never is the characters. It's always the players. "It's what my character would do" is something that warlock I mentioned advises against. There are many ways to play evil that is cooperative and fun and she has a video describing one of those ways and why she plays like that. But this isn't one-sided. The LG paladin could easily use the excuse of "what my character would do" to cause disruption with the warlock, but he doesn't. He has his own way of playing LG that compliments the CE warlock instead of conflicts.

Is there a deeper problem here that extends beyond the tabletop? It's time to start thinking of questions that need answers. You may be able to find answers through observation instead of confrontation and a solution based on your findings without adding to contention.

Quote from VanZoeren >>

If I were the paladin, I'd want to leave too. Assassinating paladins and sacrificing an angelic being for the actual Devil? I get that the world is shades of grey and all that, but that action is a pretty black shade of grey. 

Brutal honesty mode: sounds like it's your DM's fault. Are they providing any avenues besides the abhorrently evil option? From your post it kinda seems like Asmodeus is the driving force that moves your plot forward, which, no matter what you think your alignment might be, will most likely make it an evil campaign. 

 Asmodeus does seem to be the driving force right now, but it seems to be that way as a result of player choice. The DM didn't ascend from the hells and tell the players "you work for me now," the cleric made a choice that brought along certain consequences. But I do get the impression from reading the OP that the party is basically going to be done with Asmodeus once their deal with him is ended. The cleric will probably still worship him until they do her redemption arc, but it seems like this episode with the planetar was going to be the end of their obligation to him. 

I think player choice makes a very big distinction when it comes to assigning any blame. 

It's not that uncommon in campaigns to have an arc where players find themselves with an obligation towards a bad guy for a few sessions until it's resolved, but calling that an "abhorrently evil" campaign seems like a stretch. Sometimes people do what they have to do. 

If I were playing a paladin in your group, I probably would have done the same thing. I'm surprised he stayed as long as he did.

My takeaway is that the Paladin player is raising serious concerns, and is being dismissed without his point of view even being considered.

Look at it from his point of view. He started a campaign where everyone was good or at least neutral. He personally at least built his character with the expectation of a good-centric campaign, and perhaps even only wanted such a campaign. And that's okay. I wouldn't want to play an evil campaign, at least one other person in this thread has said the same. There's no reason why that is wrong, and he was seemingly given the impression that the campaign would be a good-centric one, or at least compatible with his tastes for such. Instead, to fit someone else's storyline,. it's been coopted into the party serving a devil and slaughtering masses of people. The murder-hobo comment as well as the complaint that he's constantly overridden in group decisions tells me that there is probably more than you're letting on...and that probably at least partly involves wantonly killing creatures over the Paladin's protests.

I'm not saying that can't be a good campaign to play...but the Paladin player is now in a campaign that he didn't sign up for, didn't want to play and is being ignored when group decisions are being made...or at least, he's always on the losing side of them. 

That's not fun.

To pursue another point. Have you ever been in a group where you make group decisions...and they always decide against you? You're marginalised and the group just does it's own thing? I have. It wasn't fun. It was horrible. I don't mind taking losses, you can't have it your way all the time, but part of being in the group is that the group takes into account your own wants, needs and interests as well. When you're constantly ignored and told to go pound sand, it just creates frustration, tensions and distance.

That's not fun.

The Paladin player spoke to you about these problems after showing obvious signs that there they were unhappy...and your reaction was that he was being melodramatic. When he voiced concerns that he was being consistently overridden in decisions that he felt were important with him, your reaction was to dismiss his concerns with the idea that he can't get his way all of the time, which wasn't his complaint.

Yeah, I'd advise the Paladin player to leave. They're not having fun, the party isn't willing to accommodate him and when he raises concerns, they're being dismissed and belittled. That's not going to be healthy unless people make some serious changes.

From what I read, its not melodramatic, the characters are evil, and I wouldn't play in that group. 

But... that's my choice. I don't play evil characters and I don't play with evil characters becvause I just don't enjoy it. I want to be the hero and in the company of heroes. Games with evil characters aren't bad games, just not games for me. It seems the player of the paladin is the same.

Personal note: I have quit a game over this issue (a Curse of Strahd game where the characters were sympathetic to Strahd and helping him with their actions). I even referred to the characters as murderhoboes. I miss hanging out with the people, but it just wasn't a game for me. I hope the GM will invite me back once the Strahd game is over, but its not looking likely.

I agree with those saying that this is the DM's responsibility. If the campaign was initially set up as a good, or even neutrally, aligned flavoured theme only to change to an evil themed game, then that's the DM's fault. The player has built his character around that assumption and chose a Paladin to fit. It's a bit like a DM saying the game will be set underwater only to have it morph into a game set in a desert and then wondering why the player who has a merfolk ranger get annoyed.

I think the players with the Paladin either needs to modify his character with the support of the DM (so it fits with the direction the game is going - Darkguard? Paladin of Vengence?) or he creates a whole new character.

I actually think the DM is playing favourites (has he got a crush on this player?) and making the game all about her. As a DM, you need to balance out the game so everyone feels invested, everyone has their moment to shine and everyone is happy. That's why its such a difficult job.

Your GM is a jackhole.

The characters were created neutral to good. The players chose to create good characters but the GM is choosing mass murder and angel sacrifice.

He knows the new player has been coached to be a decent player and will try to pick up what the GM is putting down. So the choice to drop the devil worship options on the player were the GMs decision. He knew it would be likely she would do it because she wants to play, and part of the social contract is that you pick up the GMs cues and not try to derail the campaign.

If it were me, I'd walk away. Not being melodramatic, I don't play in evil campaigns. Other people can enjoy that kind of thing, I don't.

A few others have said it and I will too. I don’t think the player is being melodramatic. It seems that they are just not the right fit for the group if they plan on playing an evil-ish campaign or part of a campaign. Maybe I’m just an old fuddy-duddy, but I’ve played an evil character or two 40 years ago but have no interest in playing one today.

From what the OP said it sounds more like a player preference than a character one. So changing characters wouldn’t solve the problem. 

Some blame falls on the DM if session zero made it out to be a good/neutral campaign, but then changed. But it’s not entirely their fault. It’s ok to introduce a moral dilemma to the group (should they work with an evil entity but for the greater good) but it can get dicey when all of a sudden another player wants to go down that rabbit hole full speed, like it seems like the case here.