ag0710: First of all, it's very encouraging in this whole thing that you have been able to have the courage to ask your son to leave your home after you have set boundaries but yet somehow finagle it so the relationship with your son did not need to be severed. Well done parents!
I have a 26 YO addicted son (AS) so I am a little ahead of you here. If you have not done so and you are readers then my suggestion is for several books (I'm sure there are others just as good): The Lost Years (written by a daughter who had been addicted and her mother who learned how to truly help her daughter). If you Google this there will be another book by that name so you gotta look. Another book is "No More Letting Go. The Spirituality of Taking Action Against Alcoholism and Drug Addiction" by Debra Jay. Another is "Addict in the Family" by Beverly Conyers (go to the Hazelden site to order this). I just discovered a radio show on the Internet "Eye on Addiction Radio" where one of the topics is how to intervene. This particular show's guest was Jeff Jay, the husband of Debra Jay. In this show, he talks about how to interact with our addicted loved one in the scenario you have with your son - when you have intervened and they have refused. I found this to be a very helpful show.
And pray, pray, pray for wisdom. Keep coming back here. There's lots of support and wisdom here. Don't forget Alanon or Naranon meetings for you both.