The fact that he is still using is proof that he isn't ready to change anything. Until he is so miserable that he doesn't want to live another second the way he is currently living, nothing is going to change. You maintaining contact with him does nothing other than keep you upset.
Detaching is a good thing, but you haven't detached. You have simply stopped living with him. You are still involved; you talk to him every day; you take him food; you know what is going on with him. That is not detachment.