Another mom here, with almost the same story as you and the other moms.
I'm coming in late and haven't read all the replies, but saw you already decided what I was going to suggest....sell the car, halfway house!
I tried letting AS come home after rehab, testing him daily for drugs, and it made me a total wreck. Honest, I was close to a nervous breakdown, whatever that is. He wasn't ready to quit, so he had a stash of clean urine and was actually doing crack in my own house!
He's staying in an Oxford House now, they are not as restrictive as a halfway house, but he's got 7 guys to talk to and since they are all recovering addicts, he can't put anything past them. He was SOOO lucky to get in there and it's been the best thing to happen to him in many years. Do you have any in your area?
As for why, I did the same thing as you in the beginning...I wanted to know why, how this happened. Thanks to the great people here on SR, I FINALLY realized I was wasting energy even thinking about it. There is no answer to why. There is only today and what we need to do right now.
Sounds like you are on the right track now, feel free to PM me if you want to talk or just rant and rave!
****{Hugs}}} and prayers for you and your AD! SM
PS...the post from Notsleepingwell marked a major turning point in my thinking the first time I read it. An "AHA" moment...hope you find yours, too!