My friend is considering suicide. Please help?

I swear he is the perfect child. He is abstinent. He is going to be going to college at 16. He's in several sports. He's an artist. He helps his friends in dire situations, gotten some off drugs, etc. Honor society, key club, martial arts, basketball, archery, swimming, going to a technical academy. Generally nice, no real flaw except sarcastic. Practically perfect. But, his life of doing this, his screw up friends, his cheating ex, and his mother make his life hell. Especially her, she is diagnosed with several mental disorders. He has come to the point where he has planned a way to kill her, but said he will never go through with it, all life is precious. Yet she is horrible. She keeps him grounded for life, no fun, always yells, discourages, drinks, verbally and physically abuses him, etc. She threatened his future, and everything. He has never done more than a light complaint right after, he hardly complains at all, unless he is really confiding something big, or in writing. But, I walked in on him the other day, and he was crying, with a throwing knife against his throat. He told me it wasn't going to be then, but he is really that sick of it, and to leave the matter alone. I know a lot of people show it off, but he never said anything, I wouldn't have known if I didn't walk in on that. That really scares me. Please help.