It's very hard to watch someone you care about behave in a self-destructive manner. It makes us feel angry and helpless. Neither you nor your boyfriend's parents have been able to convince him to get the professional help that he needs. You cannot be his therapist or his savior. You can only be his friend. But if you continue to be his girlfriend while he abuses drugs and alcohol, you are saying that he can continue to do things to himself that aren't part of your value system, and that you will continue to stay his girlfriend no matter what. I don't think that helps him or you.

This young man's parents need to intervene in his life to get him the professional help that he so desperately needs. Unless and until he can get sober in a treatment program, I strongly suggest that you terminate your relationship with him. If his health means something to you, you need to break this off and hope that he can come to his senses before he does himself or others irreparable harm.