I second that you go to the top of the forum and read the stickies.
Thing is, there is no WHY. He is drinking b/c he is an alcoholic, simple as that. He is pointing the blame back to you as a form of manipulation b/c he does not want to accept any blame or admit it's an issue, that would require him to change, and he does not want to do that.
It will progress. He has it planned in his head obviously, as per his own statement that he will be dead by 40.
You need face to face support for YOU. There is Alanon, Celebrate Recovery, therapy with someone who specializes in addiction, all sorts of things. Here at SR you will also find good support.
Only you can decide how long you are willing to accept this behavior in your life, and what you can or will do about it. I know I made some boundaries w/myself regarding my X husband before I made him leave. I decided I would not be around him if he was drinking. For me, for a while, that meant I would leave if he drank. Then I got tired of that. Why should I leave. So from there, I made him leave. I did not waste my breath in fighting or anything of the sort as there was absolutely no point in that.
Eventually it all blew up, but that is not the point. The point is, you cannot change his behavior, only your own.
Hugs to you. I know it's so hard, and it hurts. Keep coming to SR, get face to face support, and don't isolate, that is a form of self abuse!
We are here for you!