It didn't work for when my son came home at your son's age after his 1st rehab.
This last rehab he went into sober living house with a program for 6mos. after he left inpatient rehab.
It can't work for you or him for you to be his minder and monitor.
You will be sucked into codependency and him into his dysfunction.
Help him find a quality sober living house with a program is my opinion.