I can't speak for him, but personally -- I often drank because I felt guilty for hurting people I loved. Of course, drinking made things worse because I hurt them more. Eventually the guilt and self-hatred grew into an avalanche that I couldn't control. I got into a state of "things are too screwed for me to fix" so I gave up and tried to drown it all in alcohol.
But like someone said, he probably doesn't even know why he's making those choices. Alcoholics/addicts are insane people, and they don't always make sense.
I'm sorry that this is happening to you ... It's not your fault. I hope that AlAnon can help you through this.