Support vs Enabling

I have a 22 year old son who is a recovering Heroine/Blues (synthetic form of heroine?) addict. He was diagnosed with clinical depression in adolesence, was in juvenile detention from 14 to 17 and most recently in jail for the past 7 months for fraud ( he stole checks from his father.) My ex husband and my daughter (we are close) refuse to have contact with him at this point and I am the only family member he has contact with. He is living in a halfway house in the same town and attending meetings as required. I know he is having a difficult time as it is a horrible place with many homeless men living there. I am struggling with letting him stay with me for a defined period of time with a written agreement and requirements to offer support for him. I belive he has "hit bottom" this last time but not sure if I can know that for sure. He became a father 7 months ago and they live in another state. I would like to give him the support he needs to be successful but don"t want to fall back into the same patterns. I have not been the "Tough Love" one in the family ...