Gonna, the information we are missing is what HIS take on this is.
It sounds as though his initial justification for the affair was, amongst other things, that you were fat, that he never loved you and that OW was his "soul mate".
What does he say now?
It sounds as though he thought that this was a grand love affair of epic proportions.
What does he think this was now?
You say you mistrust your judgement because you never knew he was unhappy. That's in all probability because he didn't tell you he was, or indeed that he wasn't actually unhappy before. One of the biggest myths is that only unhappy marriages/people are vulnerable to affairs.
What does he think was the reason for this affair?
How does he view the OW now? Does he regard her as the she-devil who wrecked his life and cannot be forgiven for not loving him enough to choose him? Is she an evil woman who hurt his life and his wife terribly? Was she a fantasist with a poor grip on reality, which therefore makes HIM a poor judge of character? Or does he view her as a damaged individual and wishes he'd never clapped eyes on her?
His view of her is really telling, you know. Hating her for not loving him enough gets a zero score. Hating her for hurting you (what this OW did was actually totally unnecessary and cruel you see) is pretty healthy at this stage. The eventual aim though is to view her as a damaged individual, wish her no particular harm, but to scratch his head with amazement that he ever saw her as an alternative to YOU.
Finally, two important questions.
If she prostrated herself on his doorstep with grief that she had made the wrong decision and begged to try again, what would he feel? (as opposed to what he would SAY. You imply that he is a basically good man who you think is staying out of duty. You might suspect he'd say "no thanks" out of duty, which is why it's important to get to what he'd be FEELING.)
And what does he love about you? Set aside all the bitter and twisted manifestations of your extreme hurt, but what does he love about gonna as a human being? Why does he want you as his romantic partner again, set aside from your qualities as a home-maker, professional and mother? What does he see in you as a woman?
You seem to set yourself impossibly high standards for getting over this. As I've said before, no-one ever knows how this is going to affect them. I'd never have believed the way my situation has affected me either.
But I do have closure on the above issues, that allow my esteem to be high and to view this as a wake-up call that has brought huge hurt, some bittnerness but also wonderful gifts. Unless you tell us otherwise, I don't think you have that closure, so how on earth can you get over this and stop feeling so angry and bitter? Give yourself a break, you are way too hard on yourself.