Oh, and by the way, my son sounds VERY much like yours. We kicked him out and he's been having a pretty rough go of it but getting better now. He was also diagnosed as bi-polar a few years ago.
My logic has been this: We tried to get him 'on track' to have a manageable life (psychiatrists, meds, rehab, college, trade school). He rejected all of that in favor of street drugs. Yes, he has an addiction and a psych. disorder but no matter WHAT I do for him now, it will not help him in the long run....I will not always be here to protect him. My son, whether sick or not, has to learn how to manage his own life. HE has to choose to see his doctors and stay on meds and get good rest and eat right and get exercise.... I can't do any of those things that will help abate his illness for him. So that is how I've learned to let go -- by keeping in mind that he HAS to learn these things now and unfortunately he's chosen to do it the hard way. But guess what?! He is making some progress! FINALLY! It's not easy, and we all backslide from time to time, but I think you need to think about giving it your best shot.
((((Hugs)))) to you.