I lived in an Oxford House and it was a huge part of my (so far) successful sobriety and recovery.
While relapse is often part of people's story is not part of recovery ..... it's called active using.
YOU get to decide your boundaries, if that includes "No using or your out." There's not a thing wrong with that. I set that boundary when my actively using mother had no place to live. The rules were, no drinking and find a job. She did neither. I kicked her out. One of the hardest things I've ever done. I'm happy to report she is now 8+ years sober.
I have a few questions for you.
How old is your son?
Have you considered Alanon?
BTW, 12 day inpatient rehab sounds more like detox to me. I went to inpatient for 30 days.