my boyfriend self harms

My boy friend and I have been dating for 2 years. He's 16 I'm 17 and he self harms. He constantly downs himself and always says stuff like " I just wanna kill myself" & I always see how bad his cuts are and I try so hard to do anything I can to be there for him but it's getting to the point where I'm really scared for him and I really want to tell his mom that he needs medication or something to help him, but his parents aren't really open with that kind of thing and he begs me not to ask them about it for him but he won't ask on his own because of an incident that happened with his dad when he found out about his cutting. 
I'm afraid if I ask his mom she will just brush it off like it's nothing. My mom told his mom once but that's what she did. I have no idea what to do. Any suggestions? It kills me to see him like this.