Pock....
I used to have that fear about my ex husband when he was in his first year of sobriety. I went to group counseling, had a counselor, and worked an anon program. For me, it was a combination of the passage of time as well as getting stronger in my own recovery.
I hated that feeling of fear and remember it well. Try to remember that there is nothing that you can do and that includes worrying or recommending what you think is best. I've learned that the only recovery that really works is the one that comes from the inside.
Also...the acronym for FEAR is false evidence appearing real..........
You are not alone. I used to look at people in my anon groups and wonder how they ever got so calm about it all and didn't worry whether there loved one was relapsting. But in time, with working my own program I got to that place.
Hugs....