The short answer? Its being passive a aggressive. *We*had to build up a monster in *our* minds to justify slaying it when in fact the monster was *us*.
My ex is very P.A. He avoids confrontation and the only time he was willing to be outright cruel was when I was sobbing and he felt like I wouldn't/couldn't respond. He said all kinds of BS that didn't make any sense to justify what he was doing and I thought he was having a psychotic breakdown too.
He knows what he did is dead wrong. He wouldn't have worked so hard to try to blameshift and justify if he thought what he was doing was OK.
I would love an apology that didn't include a "..but.." That isn't likely to happen though. I don't think he can accept what he is and what he's done. He's too emotionally-stunted, weak and cowardly to work on himself and it would take a lot just to get to the point where he could acknowledge his wrong-doing and apologize.
His cruelty is a part of him that was always there. It was hidden behind the "good guy" mask he wore with pride. It's a part of himself that he loathes and now that it's been seen by me he (correctly) assumes that I loathe him too. Of course he could change that by *BEING* like the "good guy" he impersonates but he can't. He won't do what it would take to become the man he wishes he was so it's back to pretending until the mask slips again.