My heart also goes out to you all. You do have to let go for your own sanity. I needed lots of counseling to let go. Once I was able to let go (and stop answering the phone in the middle of the night and bailing him out financially) he had a very tough go of it. He lived on other's couches and the street and did drugs and refused to take his meds... he occasionally would show up back in town and get into a another facility. Every time he got out - I was like a broken record- stay on your meds, stay off drugs and I will help with housing. I could not have him come home as he was also dealing in my town.
Eventually ( 3 years) he called and said he was "willing to do whatever it takes". I engage when he does what he needs to do - no drugs and taking meds. I stop when he quits his part of the bargain. I moved him out of state to a psyche hospital - 3 weeks in patient, 1 year out patient 20 hrs a week. He lived in assisted living. I was the payee for SSI and stayed engaged and visited often.
He is stable, drug free, on meds, and happy once again!! It has been 2 1/2 years since the "do what ever it takes" day. He needed to take responsibility for his actions. Your job is to point out his choices have these consequences....(life will teach him that anyway) and other choices have other consequences ( the more positive ones).
My son relies on the NA/AA support system and in the outpatient activities he was able to learn he is not alone; others are dealing with these same issues. He was able to see the ones that were struggling like he was and the ones that were well along the path of recovery. He now speaks freely to NA meetings about the tough road and is a good role model for others.
Hang in there - preserve YOUR sanity, be there when he is ready for the help he needs, and realize this is his battle. You can help, but he needs to want it for himself. Hard lessons for us both. We are both better for learning that.
Responsibility is his, recovery is his, healing will happen for you both as he gets well. All your original parenting lessons are still within him as is your love. He knows you love him even though he says he hates you. He really hates how he is feeling and hates that the solution is so hard. They do accept tough love and even thank you for it someday. (don't hold your breathe it takes a while)
Take good care of yourself in the meantime!