I know it sounds cruel but maybe your karma is to change your friends and find friends who are trying to help themselves rather than looking for others to do their own work. I think it is part of learning to nurture and love ourselves. Being bipolar makes it so much worse because I think we feel the other's pain or at least it feels that way and it is so awful to feel helpless.
It is almost more comfortable to put ourselves in harm's way...do you agree?
If you believe in karma, then it might be easier for you to change because you can say that your friend is living through his karma and he needs to go through this to evolve...and you shouldn't hold him back.
Bobby