That's why people wait until there's someone else before they jump ship. It's just plain easier and most people just don't give a shit about anyone but themselves. Almost everyone is too cowardly to be alone, too cowardly to face themselves in the mirror. So they fill their heads with thoughts of their new person and with thoughts of justifying how their current person is a piece of shit and they just need to get out at all costs.
This is what an exit affair boils down to... They were unhappy in the relationship, but did not know how to communicate it properly, or worse, did not want to. Communicating things you are unhappy with means you then have to go through the process of doing the hard work with your spouse to work through these issues. This seems too hard, they want to take the easy way out.
They don't want to face whatever is broken in them that is making them unhappy, so instead, they blame someone else for their unhappiness.
For these types of people, it is easier to just leave and give justifications for leaving, even if that means rewriting everything. It is incredibly cowardly. Which is also why they tend to find someone else before they leave - it is always easier when they feel they have a partner in crime who "understands."
Also know that deep down, he is aware of how terrible his behavior is. He just cannot admit that, because his fragile ego cannot handle it. That is why he is coming up with every reason in the book why your relationship was terrible, even though it wasn't. I know it sucks when the person won't own it. It starts to make you feel like you are crazy. You search for things you did wrong, or things you could have done differently. But remember, even if you were the worst wife in the world (which you were definitely NOT), there is never an excuse for an affair, and he knows that!
Even if he won't say it in words, the simple fact that he chose to hide it from you means that he knows it was wrong, so his actions are speaking for him. It's like a kid being confronted by their parents for sneaking out. They might get defensive, yell, and even slam the door to their room. But ultimately all this does is confirm to the parent that they were right, and the kid is just being immature and acting out. He might not be admitting fault through his words, but he is through his actions. I know that doesn't undo his horrible behavior, but hopefully it helps you feel a little less crazy.
Slight t/j: Falc, you, BB8 and I seem to be in very similar positions given our ages, the length of our marriages, and the exit affairs. Every post you have written I can connect to on a very deep level, and it seems that BB8 feels the same. I don't know if this is sexist or not, and I don't mean to be insensitive as I wouldn't wish this on anyone, but it is comforting to know that this same thing happens to men as well - it feels like the media tends to portray BS as female and WS as male, so it's easy to get swept up in a man-hating type of frenzy, so I am glad to have seen all of your posts, it helps me see that this is more about personality type than anything else. The WS being of the personality who won't take responsibility for anything, and who wants the world to revolve around them, and the BS being the type who would give anything for it to work, and maybe often would give too much. I know not every BS is a codependent, but it seems to be a common thread. And I know Codependents get a bad wrap, and I am of course going through a lot of self-help to make changes for the better, but if people were incapable of change, and I had to choose between being a blame-shifting, narcissist or a person who gives too much, I would choose the latter every time! End t/j
Also, BB8, I sent you a PM. Hang in there everyone!