Your son reminds me of my own, he went to many rehabs and was in the revolving door of recovery/active addiction for years. He has been missing for about 12 years now, lost in his addiction somewhere.
Like you, I tried for years to help him, fix him, thinking if we gave him a loving home, good food and a job with my husband's company, that he would embrace a better way of life...and every single time it turned our home into a war zone. His addiction almost killed ME.
Today I find my peace by asking God each morning to take care of my son and then spend the rest of my day in faith that He will.
If your son becomes dangerous, perhaps taking a restraining order out may be necessary and then charging him if he continues. A person strung out on drugs can very well be dangerous and do things that they would never consider doing clean. Be safe and be careful.
Hugs out to you, from my heart to yours. It breaks our heart to watch our adult children self-destruct.