You know - when they are in crisis, they try to find a reason, an excuse, why they had to leave - something that makes them not feel so bad about themselves.
I've heard a lot of ridiculous things (me ex told me I walked too heavy. One woman here was told it was because she was too fat - at 5'8" 124 lbs!!!)
Clearly, if your H used to say those kinds of things about your kids, he didn't really cheat because of the kids. Yes, step-parenting is hard, and some people don't realize that as step-parents, they have to step back and defer to the bio parent's parenting style. And there may well have been conflict between the two of you once his kids also entered the mix. But none of that is really what's going on here, it's just a smoke screen.
In addition, his comment about your D being the "D he always wanted".......well, that's just weird, given the circumstances. Makes me wonder how much of his affection for your kids was real, and how much was "the act".
My sister's first husband was/is a sociopath - not an obvious one, but a sociopath nonetheless (read The Sociopath Next Door for a good description). One of his characteristics was a chameleon-like ability to blend in - he seemed like such a loving husband with all the same interests as my sister, but behind her back he complained bitterly about her and he never continued any of those interests once they split. (Now he's working on getting married a fourth time, and just doesn't understand why his fiancee is upset that he conveniently omitted telling her about his third marriage - the only one he didn't have kids from, so I guess he thought he could get away without mentioning it??? lol).
