Hi Tennis Pro,
Sorry for your pain. I can relate. The A is one thing, but a lack of remorse and an easy willingness (or even a thinly veiled eagerness) to end the marriage....it's just soul crushing.
I have tried hard to understand it. The closest I have come, so far, is to accept that my xWW was not the person I thought she was, and she didn't love me in the same way I loved her.
Strength to you.