jinx
Letting go is the right thig to do, and I know how hard this is for you because I have been through the same thing with my son.
My experience is that when they actually hit the streets and become homeless, as awful as that is, it is often the turning point when they reach out for a program or help to get back on track with their recovery. The hardest thing I ever did was to not let my son come home, and it was also the best thing I ever did for him and for me.
Most shelters have counsellors to speak to and access to recovery programs for those who want it. The ones I have seen have clean beds and rooms and good hot food. I actually had to go to the rooms one time with a man from the Salvation Army to retrieve my son's things while he was in rehab waiting for program, and that is when I saw first-hand that these places are very livable and offer support. I think God took me there because I was never afraid of them again.
Go to your meeting, find all the support you need, say a prayer and know that God watches over our children.
My hugs and prayers go out to you and your son too.