I’m playing a light domain cleric in a game with one other player who is playing a rogue who is about to get the soul knife sub class. (We levelled up to level three at the end of the last session.) The rogue is supposed to be this agent from an organisation that hunts monsters, where as my cleric is an enthusiastic cultist whose order sent just to lend a hand to our new boss. 
  Although I always save at least one spell slot to heal the rogue if he goes down, and was really bad at sneaking, because of scale mail armor. My character seems to just be deadlier between burning hand spell and my divine radiance ability. 
I’ve changed the scale mail for a chain mail shirt, but it still feels like my character is more dangerous than the professional monster hunter. Also the rogue does have a contact that he can buy healing potions from, but compared to my available spells, it doesn’t feel like he can keep up. 
How can I avoid being the main character? 

There is a caster / martial devide in D&D in that casters do tend to outshine martial characters. I think a lot of this is because the game is balanced around about 8 encounters per day with a couple of short rests. At level 2 that means more than have the encounters you have to make do without casting any levelled spells, however at low levels radiance of dawn is exceptionally powerful and that refreshes on a short rest.

Radiance of dawn scales with level only a tiny amount so as you progress in levels this will become less overpowered but you wil grow in power in other ways, when you get ot level 5 you get to learn fireball for example.

Regarding ways to deal with it:

A rogue is a skill monkey, so he will be good at things like scouting ahead without being spotted and opening locks and this is a valuable contribution that can be forgotten you can roleplay this by being amazed at how quiet he is and how that lock looked unpickable etc.

One approach you could do is try and concentrate on buff and control spells. If there are just two of you in the party there is a problem in that most of the buff spells like bless and aid assume you will have at least 3 party members to cast it on, and beacon of hope really shines with a very big party. Against humanoids hold person would pretty much guarantee the rogue would get at least one crit hit if the enemy fails the save but is useless against non humanoids.

If you the idea is the Rogue is a professional monster hunter and you are just helping out and a lot less experienced it is possible you could change the characters to account for that, but it would require a discussion with the DM and the other player. One option would be to have the rogue a couple of levels above your cleric, an adjustment to that would be to have the same hit points that you would have at the rogues level so the DM doesn't need to worry about you being to fragile.  More encounters per day will also reduce the power imbalance if the DM is willing to make that adjustment.

Hey, sorry I haven’t gotten back to you sooner, life kind of gotten in the way. 

So I had a chat with the DM, he wasn’t prepared to have the rogue out level the cleric. However, your role play advice has really helped. The rogue has been going ahead more and the area we were clearing out has more traps and locked doors then we have had previously. This coupled with the rogue’s psi abilities making him noticeably more deadly has allowed the rogue to be more effective. 
I’ve also being using the bless spell more, and moving to flanking positions to get rogue’s sneak attack to hit more often. 
  We are also being more active now, getting three to four encounters in rather then the two we were getting before due to caution. 
So basically thanks, for some really good advice.