My boyfriend won't stop cutting himself, help please?

Ok so my boyfriend and I have really screwed up pasts. I think that’s why it’s so easy to relate to one another. Anyway he told me he use to cut himself and that hes on antidepressants. He said he was going to stop cutting because it hurts everyone involved. I agreed with him naturally. And had no reason to dought him,Until today. My friend said she saw him cutting himself at lunch, she tried to take the razors away but he wouldn’t let her. That’s when she came and told me. I was so upset that he was hurting himself, and the worst part was, later I found out he yelled at my friend when he heard she told me. Because he wasn’t going to tell me at all. I didn’t talk to him until the end of the day because I really didn’t know what to say.
Later on the bus he text me and said he was just mad at his friend and he couldn’t take it anymore. Then, when my friend (Sam) told me he got pissed. I asked him not to cut again because it killed me when I heard. He told me he’d do anything for me. But I still couldn’t forgive him yet. I don’t know I felt like there was something else I didn’t know.
I got on myspace later and saw his status it said “I ****** up so badly. I wish I wasn’t here anymore. If anything happens to them i’d cry. If anything hurts them, I’d die.” This caused alarm for everyone. I checked Facebook,Myspace then I text him. When he didn’t answer I was wrried. Later he answered, his phone was off.. I’m still worried about him though, what can I do? Thanks.