As long as I've been going to Al-anon, I've never heard anyone in a meeting blame the alcoholic in their life for the mess. That is not to say that there is mention made, briefly, about something that occurred between the addict and their partner. Al-anon is about you. If the alcoholic wants to complain or get off their chest what they have done, they can go to an AA meeting.
His blame is HIS BLAME. You only have to concern yourself with what you do. I think if you stand back a bit and detach from your own post, you will be able to see your role in this situation. You cannot have a calm, rational discussion with an A because you are not dealing with a calm, rational person. You are dealing with someone who is chaotic, thus you will become embroiled (as you did) in a chaotic "discussion" where NOTHING gets resolved and everybody walks away mad, frustrated, and just the same as they were before any so-called "discussion" occurred.
I went through an entire day several months ago of my AH blowing up, then making up, then blowing up again. I finally drove to a nearby restaurant, had dinner, and left him to pass out. You can have the most logical rebuttals to an A's accusations and IT DOES NOT MATTER. They have their beliefs lodged in their brains and aren't about to allow anyone to jar them lose. My AH has admitted he is an alcoholic numerous times - not just to me but to others - but he continues to exhibit classic A behaviors.
I can admit I'm codependent till the sun goes down, but it doesn't stop my codependent behaviors until I am willing to work a program and get counseling. Believe me, I need both - I'm a top-notch codie.
I think Al-anon will help you sort out a lot of things about yourself. Be easy on yourself. You made a mistake, but you didn't commit a mortal sin! We all do just what you did. As they say in Al-anon, "progress, not perfecton." Please let us know how the meeting goes.