I can tell you from my own personal experience that the deeper AH sunk into his addiction, the less he wanted to be seen with me or do anything with me. I made a few attempts to get him to go places with me - it ALWAYS ended in disaster with him starting some sort of "war."
You've been put in a terrible position. He's telling you he will only attend this booze-a-thon if you don't go. It could be that the "other woman" will be in attendance, if you mean by 13th stepping that he is having an affair with another woman. It could be he wants to go alone so he can start drinking again without you seeing it actually happen. I'm only speculating here, mind you.
However, I am not speculating now: WHY? This guy is treating you like garbage. You say you really want out of the relationship. You also say you are becoming physically ill (I assume from the stress you are under). There are no such things as completely clean, civilized breakups. Well, if you have two totally passive-aggressives breaking up, they generally just back out of the relationship to keep up the appearances of how "nice" they are. But psychobabble aside, you're miserable. Yes, he is certainly contributing to making the situation miserable, but you are responsible for your own misery when you stay even though you really want to leave.
If you walk, you will be trading a known pain for an unknown pain. However, breakups are painful if we've emotionally invested a great deal of ourselves into the relationship. It sounds as if your bf has already moved on to me, so you can prolong the inevitable or you can leave now.
You love the guy, but he's an ass. How about placing a higher value on yourself, quit waiting around for him to un-ass himself, and get serious about your own recovery. I believe you will discover that you deserve better than some financially irresponsible guy who is an "ass."
How long did it take me to cut my losses? As long as it took me. Nobody could tell me when I'd had enough. I told me when I'd had enough. Basically, it happened when I no longer loved or hated him. I just got sick and tired of being sick and tired. I woke up one morning and realized life can be good and doesn't have to be lived down in a stinkin' cesspool of misery with an active addict or a dry drunk.