My friend's psychological problems have gone unnoticed for too long. This problem has come up several times in the short 14 years I've been living, with several different friends. Let me start by ...
You need to work on you.
Let him worry about himself. If he does not want help, holding a gun to his head will not make any difference. Oh, he might agree to go into treatment, but it will not benefit him. He needs to make the decision that there is a problem and that he wants to deal with it.