I'm sorry you're going through difficulties. I think a lot of that "what-if" and waiting for the other shoe to drop is a kind of parents' PTSD... we all had many, many experiences where we thought things were going well only for that illusion to be smashed by the newest crisis/drama.
What I did recently, which I found helpful, is to give this issue over to God. When I started obsessing again about where my son is, his continued drug use, what if he's had an overdose, etc. etc., I take a deep breath and ask God to watch over him for me. Because I can't. Because he's an adult and I can't make his decisions for him. I can only pray for him to make better ones.
