>>1 Do you know why he wants to kill himself?
Anyway, maybe you should try telling him that suicide is a last resort, that he should try to find another solution first. If he has a specific problem, there are always other means of dealing with it, and if he is depressed, or just doesn't want to live anymore, it's just the way he feels now, and feelings change, so it would be unreasonable to make such a big decision based on them. After all, he can kill himself anytime he wants, so it wouldn't hurt to wait and see if things will change or if there is another way. There usually is. And you should definitely tell him what he means to you and that you will help him in any way you can.
Also, you could take a look at this thread:
http://dollars-bbs.org/personal/res/1370563145.html maybe you'll find something useful there.