Here's a specific example we saw:
She used to worry about getting home to "spend time" with him. It was always a bit odd and it was clear that she seemed to think that she had to rush as if she wasn't home he'd be unhappy. But of course, he didn't make that clear if we saw him.
But the mask started to slip and she started pushing back. So he simply couldn't hold himself back. What also changed is that instead of completely humouring him, she started stopping so I was 1. invited round for an evening drink for the first time in YEARS and 2. (on another occasion) we agreed to go out for an early dinner (also first time in YEARS) and I popped by to pick her up. On both occasions, he was sulky, rude and astonishingly unpleasant when I arrived.
I think he thought that either she'd change her mind and cancel and/or that I would tell her she was being mean to him and should stay home and/or that I would feel bad for him and leave.
When he realised that I wasn't as stressed and sympathetic as she had always been when he behaved this way, he then attempted to backtrack, telling me after the drinks event that, "it's just that when things are not going well with us, I can't help it, I wear my heart on my sleeve and I'm just so upset".
He honestly and truly believed that I was going to pat him on the arm and commiserate with him.