I understand Periwinkle
I can't imagine the hurt of being cheated on if you are wanting to stay with your partner so perhaps it is naïve of me to comment, but there are resident parents who act appallingly after an affair in regards to the children. I've seen women use them as what they perceive to be the ultimate weapon against their ex, and there is no justification for it I'm afraid. Even your ex being a cheating lying bastard is no excuse for not only not helping protect your child from the fallout, but actively damaging them as some kind of vindication while you work through your own feelings.
My DH has a very similar sounding ex to yours - physically attacking me on site and pouring all of her energy for years into hate and vitriol and aggression. I wasn't even the other woman!! And she knew that he didn't want to be with her at all but had made threats which backed him into a corner, he felt (basically making herself seem so unstable that if he left her, their son would not be safe).
The poster who argued with Periwinkle expressed exasperation at her post and mentioned being polite through gritted teeth, buying father's day cards etc. That's no comparison to how some women behave and it's not fair to berate another poster for being the OW in a completely different situation.
That brings me to the OP - I have neither cheated nor been cheated on so I have a fairly neutral perspective. I think that there are no generalisations to be had, I'm sure they are just as varied as relationships that started without affairs. It's hard to ask someone if they trust their partner 100% or to quantify it like that, because nobody, OW or not, can claim to know another human being inside out, nor can you foresee every circumstance in life that could result in such behaviour.
So really, I don't think it's cathartic to reflect on anyone else's relationships, as there aren't really any answers to be had that anybody without intimate knowledge of the situation could ever answer.
Hope you're doing okay OP 