There are a few major issues I can see now with time and the help of a good IC.
First, exWH has had a life long a drinking problem and I never really saw how much alcohol impacted him. He was highly functional and likely drank a lot more than I ever knew. I believe alcohol is one of the things that attracted him to the slunt as she is an immature party hag who would rather throw back shots on a work night than what most ordinary, non alcoholic folks do.
Second, the weird feeling that exwh's parents always gave me was my gut telling me that they were incapable of raising a normal person. ExWH always tried to distance himself from them, but he couldn't. He was as weird as they were, only I didn't want to see that.
Third, the fact that he never admitted he was wrong during an argument or would say "I disagree/you're wrong" in response to my telling him how I FELT was a major red flag and sign of narcissism. I unfortunately didn't know that back then.
And finally, that I was ripe for a narc and was horribly co dependent in my marriage. I over functioned to the nth degree and let him slide on most things that an independent partner would have demanded.
It's been very hard to realize all of these things due to a combination of me not wanting to see and my exWH being one of the "good guy" narcs, often referred to as "covert". The description everyone always gave of him, myself included, was "he's one of the nicest guys I've ever met.". That prevented me for a long time from really seeing him sans the narcissist mask he likes to wear.