The thing I'd be worried about is how he treats you.
I think consulting a lawyer is a very good idea.
He is likely drinking a lot more than that one half bottle every four days. That was probably the third bottle, you just didn't know it. Or he has another stash. Regardless, you deserve better.
I'd stay out of monitoring his intake and I'd definitely stay out of his relationships with other people. You have plenty to deal with in your own relationship. Have you been to Al Anon or counseling for yourself?