To have done what he's done, he's not a person with integrity or empathy.
Integrity and empathy would be required for him to ever admit he's treated his stbex spouse despicably.
But if he had it integrity; he wouldn't have behaved that way in the first place.
Loads of people aren't good at ever admitting they did wrong, if they even admit it to themselves in the first place. He's one of them. Probably hasnt even admitted it to himself.
He was probably cruel to you on top of the affair because affair-havers have to build the victim of their affair up to be a villain in their head (and usually in the narrative to their affair partner).
You must be the villain of the story, not them. They are always the hero of their own story. The side effect of being framed as a villain, is that they resent, feel antagonistic towards, take out everything etc on you & feel.justifoed in doing so.
I suppose there's a bit of Darvo in it too.
When someone's character is like this, you won't change it. Focus on recovering from it, yourself. They're shit people and there's not going to admit they're shig people.
Oh and don't ever do any favours for him again
Ever.
(You might find it useful to change his name in your phone to "piece of shit, scum bag, low life , moral vacuum sociopath").