I am sorry. I understand how you feel. It is so confusing to those of us that aren't capable of it. My IC says I will never get it, and he will never get it, never say sorry. I am not like that, my brain is not like that- these people are broken. There are no answers that will ever make sense.
My situation is similar. I had no idea my STBX was unhappy and no idea he was having a LTA. Then, he dropped the bomb on me and confessed. I was shocked, had no idea. He too would be with OW and then come home and play great husband and dad, flinging 'I love you' around. He was/is having A with a known swinger, pot head, xtasy using, overly litigious, plasticky, 2x divorced, narcissitic skank that he met on Ashley Madison. NICE! Yes, as they say....they do always trade down...
When we have talked since DDay, he is like a robot that is in a cult, but the robot brain they gave him is only a 13 year old boy brain. He is not who he was. It is like the twilight zone. He says things that sound so crazy, but believes himself. He absolutely 100% does not get it. Does not get what he did, why he did it, nothing. Like talking to a wall, so I stopped talking to him and stopped trying to understand why and how. Because he is F**ked up, broken, ruined, unworthy.
Through IC, I have gotten good information and feedback. They can shut it all down. They can justify it in their own minds while they are doing it without thinking they are hurting anyone. Like an addict, they will do whatever they need to do to get the sex,drugs, ow, excitement, whatever. It is self medicating their own pain. Then they put up walls to protect themselves from the guilt. If you run away, you can try and pretend and forget.
I know it is all going to come crashing down. It is going to be ugly. I might even feel bad for him. Or not.
Cowards run away. Mine was a coward. It was easier to run away at the point he told me how far deep in the rabbit hole he was. He couldn't handle it. The whole thing was like something a high school boyfriend would try and pull off. Not well thought out, naive, overly simple. He is trainwreck waiting to happen. He is just a scared, pathetic 13 year old boy who is clueless.