In reality, you do not have the power to stop him from using and you do not have the power to stop him from overdosing.
Whether you are with him or not, he will do what he is going to do. Addicts deflect, they twist everything around, they blame, they attempt to guilt others.
He is a very sick man, and, there is nothing you can do about.
I really do not see anything of a positive nature that he has to offer you, I guess I'll just go with "Love Is Blind".