missbea, there is no solution for his problem that can come from you. There are, however, ways for you to avoid the heartache that will soon follow. It is your choice to have a short-term heartache of saving yourself now or commit yourself to even worse heartache for years, if not the rest of your life.
Just be thankful that you found out before you got married. Or worse, got married and had children with an addict, like a lot of us did.