Good for you for sticking to your boundaries.
I cant recall the age of your son but i know that for most young adults once they get out on their own, have their own job, their own money, their own responsibilities that they have more reason to keep their lives together because they have a personal investment. Even without the drugs at some point all parents have to let their children stand on their own two feet. It doesnt mean that if you see him working hard that you cant help but it would be in your own way and under your terms not just giving him an easy place to land. Think of this which would make you work harder - living at your parents home, having a nice room, and good food on the table or living in a half-way house with a bunch of strangers? I would suspect that if he is serious about recovery that he will get himself out of the 1/2 way house much faster then he would get himself out of your home.