Actually, I usually tell people to be cautious about diagnosing their MLCer during MLC if they weren’t like that before, because MLCers can be temporarily so strange. But there are some who clearly had serious issues from the beginning and yours was definitely one.

There’s two kinds of WAS - previously good spouses having a bout of temporary insanity, who may return to their right minds at some time in the future, and those who have a serious character defect or personality disorder that allowed the cheating in the first place but was also evident in their prior behavior. My ex’s narcissism was at the root of his cheating, and is much clearer in the rear view mirror and in his ongoing treatment of our children.