Welcome to SR!
My response will be brief and think about this statement before any decision you make and it will help guide you in releasing the guilt and fear you feel associated with his addiction.
You didn't cause it, you can't control it and you can't cure it.
With that being said.... let him go for awhile... the next person he shacks up with will eventually let him go and so on and so on until he hits his bottom. Think of your children and self first! It's painful at first but the peace is like a gift from heaven!!!