I keep trying to let go, let God, but is that all I can do?
If you could actually do this, you would be way ahead of the game.
Focusing on you, becoming a stronger you, means that you will no longer enable his addiction by trying to "help" him to get better. Recovery from addiction MUST be done by the addict. Alone. There is nothing we can do except stop trying to help.
I read the best thing the other day about trying.
Do or do not, there is no try.