So here it is in a nutshell: People leave alcoholics. That's what happens. Alcoholics get left. They get left in bars. They get left on the side of the road. People tire of alcoholics. They wear out their welcomes. They grate. Invitations are not extended. Their subscriptions lapse. It's like, not your fault. It's a natural law. It's not even personal. You can tell him that. You can tell him that it's no hard feelings, it's the nature of the thing.
It's a classic progression. The alcoholic starts out with stuff, things, people, family, job, network, a whole world. One by one they get snipped off. Things and people disconnect. The alcoholic's world shrinks.
But he doesn't know that yet.
He may feel surprised and indignant when those around him first begin to get tough on him. Your leaving, or your visit to Al-Anon, and your putting up of serious boundaries, may be his first inkling that he's sliding down the mountain. Or maybe what happens first is the bar at the golf course becomes less friendly and eventually there is an incident and word reaches him that he's not welcome there anymore. Places he used to go, they say, well, he's not really all that welcome anymore. We kind of got tired of him. The trouble he brings. It's just not worth it.
And so it goes.
The main point is the simplicity and clarity of it: If he's an alcoholic, this is the way it's going to be. And he might not agree that he's an alcoholic. You might be the only who who says it. It doesn't matter. Call it anything you want. Call it chronic unfitness. Call it mental cruelty. What's important is that you are true to yourself now, and that you trust your own reactions. And you recognize that, if indeed it is about alcohol, most likely it's just going to get much worse before it starts getting any better. So you might as well plan now to get out, or, if not to get out, to at least radically shift the terms on which you live with him.