Somewhat this is all about your lack of acceptance of his drinking. You have acknowledged that you cannot stop him from drinking, yet, you continue to play detective so you can say "Aha, see, here is the proof, I got ya". And, I would assume that playing Sherlock Holmes has not stopped him from drinking, so, I ask: What's the point?
I believe that you posted that you are going to stick with him, drinking or not, so, why not just accept the fact that he is an alcoholic, and, figure out how to live with him.
Go to meetings, work on you, he is an adult, he will do what he is going to do, confronting him does nothing to improve the situation, for you or him.
If the meetings do not help you, then I would consider therapy.