((Omnom)) - I'm no doctor, but it's likely the combination of the alcohol and xanax. You stated that he knew he shouldn't drink while taking xanax, yet he does and you have become his punching bag.
His not remembering is a cop out, IMO, and I am a recovering addict so I know something about that. I also have loved ones who are still using, and had to learn about boundaries and what I would, and would not, tolerate.
I highly recommend you check out the friends & family/substance abuse forum. No one deserves to be hit, for any reason.
Hugs and prayers,
Amy