Kitty, I agree, time for him to GO. This is NOT beneficial to your son.
If his mom is 'so concerned' why he can stay with her, lol You know that nothing you do or don't do will make him use or keep him from using.
Sounds to me like he is 'avoiding' doing anything. Looks like one more time you will have to be the one to put a 'time limit' on him.
What he is doing is not conducive to peace and serenity for you or your son.
I am so sorry you are experiencing this especially at this time of year. Prayers going out to you and your son from New Mexico.
You are strong and I know you will get through this with grace and dignity as you recovery is shining!
Love and hugs,