Making my character snap

And I want him to snap pretty hard.

My character is part of a group of teenagers who are basically playing "hero" (most of them having quite noble intentions, with him being an exception) to save their parents during wartime. This particular character is very childish - like a big puppy - and at first only sees it as a huuuge adventure, like a game, and when he finally gets serious about it and wants to help out more than he has been, he gets smacked down by the situation. He is able to recover from that, only to have his closest friend in the group get killed.

I'm thinking this, in combination with his own earlier injuries and having to watch what's happening to everyone around him makes him snap. PTSD is an obvious disorder he'd have, I know that, and I'm also planning on him struggling with feelings of helplessness and gradually becoming extremely dependent upon his older brother, who he is completely faithful towards.

What I'm also toying around with is A: a gigantic nervous breakdown (complete with a violent outburst or two) after his best friend's death, and / or B: a conversion disorder involving an injury he receives early on that only shows up when he feels completely overwhelmed.

Psychology nerds, help me out, please? Do I have something believable here, or do I need to think this out more? Anything else I can use? I don't quite expect him to come entirely out of it by the end. Any suggestions or help you have for me are great.

Thanks in advance~

This particular character is very childish - like a big puppy - and at first only sees it as a huuuge adventure, like a game,

This particular type of character can usually snap pretty quickly to the point of major meltdown. Teenagers have this to an art, come on you've been one. And in his situation its even so much easier to toy with him.

What I'm also toying around with is A: a gigantic nervous breakdown (complete with a violent outburst or two) after his best friend's death, and / or B: a conversion disorder involving an injury he receives early on that only shows up when he feels completely overwhelmed.

I vote for the A: Nervous breakdown. It seems to me much more realistic like this. Everyone has a predisposition to it, especially a teenager who faces reality.

Sounds believable to me. I also vote for the nervous breakdown for the realistic factor. Plus, it'd be much more fun to write.

I'd say a mixture of both. Have B be an indicating factor that he is on his way to a mental breakdown, and then let him snap.
That sounds like an episode in House where we found out that his pains in his leg were a indicating factor of his guilt. You could have something like this, and have the pain become more and more frequent as he becomes more and more depressed or stressed out.