Any break-up is difficult and usually more difficult on one person than the other.
You should never stay with a person who you don't want to be with, simply for their sake. It isn't fair on you and in the long run it isn't fair on them either.
It seem like your ex does perhaps need some help through this situation, but you won't be the best person to deal with that, if anything it would probably be easier for his sake and your own, to cut all contact. The things he is doing and the way he's acting is going to be effecting you, and it's not something you need on your shoulders. Him telling you about suicide attempts/self harming is unfair and I know, as hard as it is, you need to say "I don't think I can help you with this, but I think you should speak to someone who can."
You're obviously still in contact with his Mum and she is aware of the way he is behaving, perhaps you should give her a call or ask to meet her, without your ex around. Let her know you are concerned for his safety and well-being and that you don't want a relationship with him, and you think that him searching through your room/needing to meet up on your breaks, is all a bit unhealthy.
But if you go through with that, you need to stick to it, you can't then confuse your ex more by texting/facebooking/emailing/skyping/phoning/ contacting him in any way!!
Best of luck,