Scared to leave a relationship?

[KMoon]

Less than a month ago my best friend introduced me her cousin. He was a very nice guy and we started talking, well, and in less than a week we were dating.
Now, 3 weeks after we first met, I've realized he's not the nice guy he seemed to be.
Last week, we were chatting and he got kinda depressed and started taking about sad and BAD things, until...
He told me he had attempted suicide twice in that week.
Now I'm scared that he is not who I thought he was (I know it seems like a movie phrase or something but I'm really scared) and I'm scared that if I ever break up with him he will attempt suicide again.
Fun fact #1
Her cousin (mi best friend) is also depressed and self-harms
Fun fact #2
This guy also told me he gets violent sometimes.
Fun fact #3
He told me this three days after my house got broken in (I'm still very affected by it) and he told me although I begged him not to.

PS: DON'T even think about telling me the "talk about it w/ a grown up" phrase, if he ever finds out I told someone he will most probably get violent and attempt suicide

I feel kinda alone and depressed, I mean I'm generally a very positive person but I can't see the bright side of this...

[Typhlosion]

I've realized he's not the nice guy he seemed to be

Does that mean being rude, being a dick, or something like that or showing his problems to you? If the latter, that doesn't necessarily make him not nice...

Either way, if you do not intend to pursue the relationship, nor intend to help him, then by all means break up! And, hate to say it, but also talk about him with a responsible adult. Really, this person may be in dire need of help and neglecting that doesn't even sound like a good idea.

On the other hand, maybe the guy was looking for someone trustworthy to share his secret, not even necessarily a personal/intimate relationship, but wants someone's support, and you can try and help him.

[KMoon]

The problem is that he seemed to be a normal, average boy that liked me, and he ended up as a violent, depressed guy that attempts suicide at a daily basis.

I'm actually trying to be with him but I'm not sure if the boy I like is HIM or he just pretended to be happy when he was with me.
I also want to help him, but I don't know how.