I am very sorry you are going through this and for the difficult time your son is having. I forget sometimes that not every single person feels the same about my children as i do in that unconditional love type of way. My AH will be the black sheep tomorrow. I get it.
Unfortunately until your son decides its time...for him......to work on his recovery he will not have success. It sounds like he has went through alot and has some underlying depression he is trying to self medicate? If thats the case maybe therapy would help him work through some of the depression. Will it cure his addiction? Maybe not but it could not hurt.
Good luck and many blessings to you both.