Getting the courage to say no to buying his beer is step 1. Preparing yourself for what the reaction might be is step 2.
I didn't realize there was that 2nd part for a while and I thought that if I could work up the nerve to tell AH no, set a limit, stand up for myself etc... that would be the end of it.
I had NO idea the level of verbal abuse, emotional abuse/manipulation etc... that would follow.
I am not suggesting that it is automatic that your AH will react similarly, I just wish I'd listened better or better prepared myself for the reactions that would come from him. Being able to blindside us, project, deflect and put the focus on any and everything besides themselves is a gift that A's have and I was not prepared to deal with that for a long time.
You are right that your AH will probably turn the focus on to your shortcomings, your weaknesses etc... Think of the things you are most insecure or even ashamed about and prepare to have him throw that all at you. If you prepare for the worst, it won't have as much power over you.
Hard as it is to not take it personally, try not to. He needs to protect his addiction and the surest way to do that is to attack you. My AH was also a master of interrupting, trying to change the topic, dictating how, where, when and with what tone I was allowed to speak. Anything he could do to steer me off course when I tried to set a limit or address HIS behavior, he did.
You are wise to be here and be preparing yourself to confront him. Among my many failings is the fact that I hoped over and over and over that if I could explain or express my concerns in the right way that he'd "get it". I wasted sooooo many years on this. He probabably heard it all the first time I said it and his reaction then should have told me all I needed to know.
One mistake I made repeatedly that harmed me was making threats that I never, ever followed through on. I threatened for years that I would walk away and leave him and not look back "if" he did x, y or z one more time. So he'd do x, y or z and then I'd break my word and stay. Obviously that kind of waffling on my part told him clearly that I was full of it and that I'd never leave.
Good luck to you...