I'm sorry to hear that. I just had a similar situation happen to me. My ex was a regular pot smoker and social drinker (except in my case my ex was only using coke behind my back) and the truth is, you can't change them. I was foolish to think that myself alone was a good enough reason for him NOT to be doing stuff like that. He even told me things like that but it's NEVER true. When it comes their DOC, guess what's more important in the end?
Addicts will always find a way to justify their reason for using. You can choose to stay with him but being with an addict is a very painful experience unless they can stay sober 100%