I am happy for you, unhappy spouse. Maybe you are a little happier too!
Even if he relapses tomorrow, (worst case scenario), you have received some validation that you weren't crazy, living in left field, or off the mark completely.
So no matter what...you've gained something that will never be taken away. I hope he continues on with his progress! But you have something you never had before, progress with him in accepting that it has been a problem. It's no longer in your head, no matter what the outcome. Validation. Scary? Yes! But validated.
It's a win win for you!