Maybe this is time to slow down a bit and focus on your life. Is there ANYTHING else you can be doing right now besides focusing all your energy on your son, your opinionated family members and the problems that addiction have caused in everyone's life?
When I find myself consumed with things that I can't fix or solve, or when I find that I am stuck trying to find the answer to the question:
"What is the next wise step for me to take?"
I try to slow down, be still, listen & focus on something else. I watch how the situation progresses without getting involved.
You made a decision. Even if you have some regrets, unless you have put someones life in danger, why not stick with it and see what happens. None of it is going to change the past, make your sons drug problem go away or fix his current problems. He is where he needs to be right now. So step back and let nature take its course.