Just an update:
And now I'm single.
I don't entirely know how I feel about this, but I think it's OK.
Michael said he has been a bad partner; I told him he hadn't been a partner at all.
He said that he didn't want to break up with me because it would make me sad; I told him had already made me sadder than I thought was even possible when he left me for MacMurray.
So I told him it was done. Until he gets himself sorted out, he shouldn't be dating anyone, and I am not OK with long distance, and I'm just relieved that we've talked it through. I'm going to miss him, but I had the worst of my grieving done by the time I had moved out (peak awful on move-out day, as I finished boxing up the last of "our" things leaving "our" house where I had planned to live together with him for a much longer period) and now it just feels good to have closure. He's having his sad now. I don't know what he was expecting, but I left like he left me when he accepted the job at HIV North, and it's like he's finally realized what he's done (or maybe he just regrets that now I've left him).
He wants to come up with some kind of ridiculous shared custody arrangement for the cat though. Which is simultaneously adorable and unrealistic and crazy (also excellent Michael Kenny adjectives).
The door is open, if he were to work out the issues that need working on, that in a year or two years or three years if we're both available and interested that we may get back together. But until then, all bets are off.