Justjo, my son is an addict and I have been where you are and understand.
It sounds like you are making some good moves, especially not letting him come home for a visit unless he is clean, at least for the visit.
I might suggest a boundary I added to this for myself, and that was that my son was not allowed in my home unless he was respectful to everyone there. No tantrums, no sarcasm, no angry outburst were allowed. We could talk about anything he wanted to discuss, as long as the conversation did not become heated and disrespectful. If it did, then he had to leave.
That boundary applies when he is clean and sober also, and to anyone coming to visit in my home. It's not about controlling others, it's about what I will and will not tolerate in my home. They know this and get to choose whether to come or not.
This sounds cold perhaps, but I learned that if I did not respect myself enough to have boundaries and enforce them, that nobody else would respect me either. It works.
My prayers go out for your son, I know how hard this is to watch and hope he finds a better path soon.
Hugs