Excellent advice above me. I guess what I would add is the 3Cs:
I can't CAUSE addiction
I can't CONTROL addiction
I can't CURE addiction
Because nothing you do is going to change whether or not he uses, then what I learned was there were things I could and could not live with.
I could live with - withholding money.
I could not live with - withholding food.
In either case, I was not going to CAUSE, CONTROL or CURE his addiction.
I would suggest not to get too obsessive about it - just do what you need to do.
((hugs))