TBH I think there is no black and white answer. There are of course situations where both parties treat the ex appallingly both during the affair and once they are together. However I also think that when you read posts like one above where the ex never moved on, screamed at people down the phone for being friends with the ex, gets themselves arrested and generally behaves in an extremely undignified manner it’s not hard to see why the marriage ended in the first place. I know that view won’t be popular on here but often the situation just isn’t as it seems.
I know a few, one was a friend’s dad who had an affair with the same woman throughout her childhood. To the extent that OW even used to ring the house to speak to him, and would identify herself to the DC. 
the mum though refused to divorce him because she said she’d been married in the eyes of god and her vows were sacred. However, after the kids left school she divorced him and he moved in with the OW straight away. However after six months she threw him out and he went crawling back to his ex who told him to do one. Have no idea why the OW threw him out after such a short time of being an actual couple though, perhaps she’d just been the OW for far too long and moving into an actual relationship just didn’t do it for her, I guess we’ll never know.
I do also know of a couple who got together some 30 years ago and left their respective partners for each other. Moved in together with her DC, and are still together years down the line. I have no idea as to the circs, although I do know his wife was very seriously ill and lived in a home, I find it difficult to judge him if he found love somewhere else as she didn’t recognise him. He never divorced her and continued to visit etc. But their lives had in truth separated years before. It’s perhaps not palatable but it’s true.
Also I know a woman who was the OW for 40 years. She had a child with him and everything, but his wife used to threaten to kill herself and the DC if he dared leave. This was confirmed by the DC, and when she died they remained close to their dad and to the OW. And before anyone says that perhaps she was driven to it by his affair, that’s stil not an excuse to threaten to kill your children.... I felt sorry for the OW though. She never really got to be part of a relationship, and I do think that often once someone has been in a situation for a long time its harder to walk away, as much as we like to judge.
And lastly a friend of DP’s dad left his mum for her sister. They stayed together and the sisters stayed close until the sister died a few years ago. The mum has since remarried someone else and says that she and her ex were never suited in hindsight.