I don't create backup characters or something like that, so that is not the problem here. I think of a character concept and put it on paper. I get really excited about playing this particular character while he is in the making. But after I put everting on paper, his backstory, class, stats, his character traits, bonds and flaws, the excitement vanishes. And I am not sure if I even want to play this character anymore. Sometimes I only realize after the first session, that I don't really want to play this character. This is now the third time this is happening (not in the same campaign). I sent the DM my backstory yesterday (the campaign hasn't even begun yet) and now I sit here, wondering if should make a different character instead. Or If I should change the class. Or if I even like the character traits I gave him? Maybe it has something to do with my last two campaigns, who both fell apart after a couple of sessions? 

How long have you been playing D&D?

Do you have a plan for the future of the characters?

What kind of level do you develop the characters?

There are a lot of factors, if you could expound a little more on you and what you do for the characters, that might help us.

I have been playing D&D for about a year now. I plan for the future of my characters, but I have difficulties coming up with character arcs. 

What kind of level do you develop the characters?: it depends on the character. Some have more backstories, some less. But generally, I give them a lot of backstory, lore, ties into the world, etc. I like making complex backstories, and I find new stories easily. The only thing I struggle a bit at right now, is coming up with personality traits. But I am getting better at that. 

There could be a planty of reasons on you to feel that way. I can't give you any accurate answer on why or how it happens, but I can try to enlight you for some possible things that might happen:

Maybe you are just the type that enjoy creating a narrative, so you get too excited creating a character but didn't feel the same way on let that character being affected by a co-narration of its story when the game starts. If you felt that this could be an answer, try to focus on creating lots of chars to enjoy that process. Maybe you can try to DM and make it on lots of NPCs, write your own adventures, full of settings and characters.

Another important thing: try to empty your mind on the tousands possibiltties you may enjoy in a character concept. You certainly would enjoy lots of them but as a player within a session you must choose one to stick on. That don't mean you can't create another ones and you can keep playing that one and meanwhile create backup chars or just create them for fun.

You can also try to put less efforts on planning that concept and create a char just with the basics, letting it full of conceptual gaps that could be filled during the game as the narrative progresses. That work pretty fine on me and I feel lots of fun on discovering who that character really is and how it build its own story. Maybe begin two campaings simultaniouslly, with two different chars but similar one to another, than in some time you will see how the narrative progress can build so much difference within them that meybe you will find another fun beyond the concept creation.

Or you can have a conversation with your DM to try shorter adventures where you can choose new character within one and another. If you and your party felt confortable on that I don't thing you must loose any fun that the game can offer. Most players would like to rise their char levels from 1 to 20 and maybe more and see how that progress goes, but its totally fine to prefer more the concept creation than that and it seems thats your case.

Maybe you can try doing less and letting some of that come through during play?  You could be developing too much then feel like there is nowhere to go or to grow with that character in the campaign. 

Or you are just restless and eager to try new characters and just want to keep trying different things. I do that myself, I have like 50 characters on DDB but I’m only playing one right now. Making characters is almost as fun as playing the game for me. 

My advice would be to try underdeveloping your character. That may sound lazy and counter-productive, but what it does is gives your time to make decisions about your character while you are playing them, based off how you enjoy playing the character, rather than trying to stay true to a concept you committed to paper before play began. 

Remember, the adventure is the thing that happens during the game, not during the backstory. Keeping your backstory somewhat open allows you to tailor it to the kind of game you find yourself in, rather than leaving you with a character you lose enthusiasm for because it doesn't fit with how the game tends to be. 

Backstories can still be complex, but you have the added bonus of making them complex in ways that go along with the things in-game that you already care about, that are maybe even based on campaign events that were entirely player driven, giving you that extra degree of authorship over them. 

A good example is Luke Skywalker. He's a far cry from the General Starkiller that first appeared as the main character in George Lucas's early scripts of Star Wars, and going into A New Hope he might not even be that particularly complex or interesting, but the character was changed during production of the movie to fit the Joseph Campbell modeled monomyth-style epic tale format that they ended up going with. And it works a lot better. Luke starting out a little more tabula rasa as a backwoods orphan kid allows the story he takes part in to shine, and he becomes more interesting, more of a character, because it's his story. His actions in the story, and the choices he makes are much more interesting than his 19 years on a moisture farm, which is why Luke grieves for Uncle Owen and Aunt Beru for exactly one scene before getting into the adventure. 

I guess that's my TL;DR. Instead of being like season 4 Tyrion Lannister, try shooting for Episode 4 Luke a little more. 

There's not really a question here. That said, I think your dilemma is fairly common. I am always making characters. Sometimes those characters seem cooler or more interesting or even more suitable for the challenges I'm facing in the game but it's disruptive to the other players, the GM and, very often, the over-arching story to change characters. You'll just have to settle and play something eventually. It might be worth your while to look into DDAL or some other style of game where you are playing session by session so you have greater opportunity to play different characters for shorter periods of time instead of locking into one for an entire campaign. But yeah, players often make way more characters than they'll ever play. 

The following is a generic saying that applies to any situation when someone is bored.   "Boredom is a byproduct of a lack of effort".   Your character is only a vassal for your creativity. 

Now, don't take that as a criticism, but an ideal of how to improve your gaming experience.   When you play your character.  Don't look at him/her as a book of stats.  Look at him/her an infinite grouping of possibilities for answering puzzles, situations, and combat encounters.   

It's the difference between a character saying.  "Me Grog, Me pound you, you die.  Me Grog".  Or a character utilizing their unique abilities is creative ways to create amazing situations for yourself or the group you are with that are both interesting and in many cases kick***! and unexpected.

It's not the tool you are working with that makes the differences.  It's how you use that tool that can make the biggest difference.  Your character *is* a piece of the campaign puzzle.   It's your job to best determine how to use him/her in your current adventure that is both fun and exciting. 

Quote from G3ralt >>

but I have difficulties coming up with character arcs.

That sounds like you might be creating fully developed characters that don't really have anywhere to go. Their arcs are already completed before your first session

There are ways to counter that:

1) As CharlesThePlant said above, do less work on your backstory. Make sure to only flesh out the character's history to the point that they would just begin adventuring. Luke in Episode IV is a classic example -- when the movie starts, he's done nothing but zip around in his land speeder and bullseye womp rats. Rand al Thor had done even less than that before he was thrust out into the world

2) You could take a cue from M Night Shyamalan. He originally wrote Unbreakable with a much longer plot, but then realized he only cared about the first act... so he just ditched the rest and expanded that first act into the whole film. So write your fully fleshed out backstory, find the spot in it at which all the pieces you need are in place, and just ditch everything after that point. Let the campaign determine what happens next for the character

3) Leave some mysteries. These can be things your DM will eventually answer for you (if they're willing, of course -- don't force your DM to do more work on the campaign than they want to do), or simply questions that you plan on answering later as the campaign unfolds. I'm playing a character like that right now. They started out as a fighter, became a Rune Knight at 3rd level, then multiclassed into Aberrant Mind sorcerer at 5th. All this was built into their backstory -- they're not fully human, and the sorcerer levels and abilities are their non-human side beginning to come out -- but the exact details on why it's happening and what they will eventually become are things I still haven't committed to yet

Quote from G3ralt >>

I have been playing D&D for about a year now. I plan for the future of my characters, but I have difficulties coming up with character arcs. 

It depends a bit on the style of DMing/playing, but by and large character arcs work best when they develop organically. Don't plan too much beforehand, just take what the campaign hands you as you play through it and riff on that. What happens to the party is mostly up to the DM; how they handle that is up to the players. 

Generally my advice would be to ask the DM to give you whatever info they're willing to provide regarding the upcoming campaign, and to create a character around some of the things you'll expect to be useful specifically that are also things you think you'll enjoy doing. If talking people up is going to be important, consider taking proficiency in a few face skills and think of background reasons why the character would be a smooth talker. If exploration is going to be a thing, think about outdoorsy abilities. Not everything has to be accounted for and your character doesn't have to be an absolute specialist, but it'll probably help knowing there will be stuff in the campaign that's in your wheelhouse and you can take a leading role in. When you expect good things, you're usually more excited about what's going to happen.

In general PCs should have plot hooks, not planned story lines, and rather than starting thinking about "what is a cool background", start with "what sounds like it would be fun to play/RP?"

I know this doesn't necessarily solve your problem... but maybe you should try DM'ing a few sessions for your friends. I'm sure your DM would enjoy the opportunity to be a player for at least a session or two. If you find yourself constantly wanting to explore fresh, new characters... well, being a DM gives you a lot of opportunities for that which players don't get. Add these characters as NPCs... they only have to stick around as long as you feel like and you don't have to worry about making all these characters fully fleshed out, battle-ready characters since they can fulfill other roles as well.

Probably not going to solve your problem, but there is a non-zero percentage chance that this is exactly what you need.

Quote from TransmorpherDDS >>

I know this doesn't necessarily solve your problem... but maybe you should try DM'ing a few sessions for your friends. I'm sure your DM would enjoy the opportunity to be a player for at least a session or two. If you find yourself constantly wanting to explore fresh, new characters... well, being a DM gives you a lot of opportunities for that which players don't get. Add these characters as NPCs... they only have to stick around as long as you feel like and you don't have to worry about making all these characters fully fleshed out, battle-ready characters since they can fulfill other roles as well.

Probably not going to solve your problem, but there is a non-zero percentage chance that this is exactly what you need.

thanks for the advice. I appreciate it :-). I thought of trying to DM a week ago or so, and I am currently writing my first adventure! So yeah maybe that really is the solution.