IMHO only & you certainly don't have to listen I don't know.
What if you let him move out. See if he can make it on his own. It might be a good test for him. Make him be more independent.
If he gets into more drugs then you could look for a good rehab for him like a 30day facility. I don't know much about them.
But maybe if he realizes he's on his own it might help him.

Just an opinion.