Surprises me that the rehab allows this. I know my kids got kicked out for far, far less. Using was generally taken as a sign of non-compliance.
Do wish him the best, and hope he finds some lessons in this.
Do you attend any meetings yourself? I found the more I concentrate on the shortcomings in MY recovery (and Lordy, they are many!) the less "mind time" I have to wonder about my addict's recovery progress.
I do wish you well.