I would tell him to call you in a year and to let you know how things are going. Basically he is going to do what he needs to do, and all the money in the world is not going to buy him time. The hardest thing in this world is to let someone you love go. It is going to be a long and hard road for him to travel before he is really clean and sober. He will be spending the rest of his life in recovery.
You are still there by his side no matter what you are or not doing. Still watching the consequences his of drug abuse. He sees that! Obviously the tough love approach didn't work if he is detoxing now. Take the time to see what you really want and deserve in a relationship and see if he hits the mark.