Dear ISO, I understand your fear and concern. Relapse is common in the early days if they are not in true recovery. You did the right thing in telling the probation officer. You need to be STRONG, meaning do not mince words with your son when you deal with this next week."legal" may mean spice or bath salts, both so dangerous in their own rights!
I do not remember what DOC your son was on, but all I know is you have to believe the actions not the words. Your son is still so young. You MUST hold your boundaries. There are programs as you know that you can enroll him in and he cannot leave if that is the next recommended step.
My prayers and my steps are right there with you from Mamma Posse member TT.
Love
TT