I think if he’s only been using for 4 months, it wouldn’t be that hard to stop right.
At some point, I think you have to have the conversation with him, because as Faith said, some people can deal with partners using in marriages. I couldn’t, and it sounds like you can’t either. And nor should you have to. You didnt sign up to this.
You need to choose your time though, zero point talking to him if he’s had a drink or is high, and the come down is probably also a bad time. TBH, only you can tell when is the right time. But you need to be safe.
Does he have lots of friends that do it, do you own a house together, etc. A magic wand to go back a year would be awesome right, but unless he admits an issue, or decides that he is going to stop because its upsetting his wife, this will just continue. I feel so sad, why does this have to happen to good people 🙁 xx