I think the thing with affairs is that people will often project their own feelings/reactions to someone else’s situation.
So if you’ve been devastated by an affair then the assumption is that everyone is devastated in the same way. Conversely if your affair led to you having a better relationship and your ex moving on successfully, you assume that they weren’t devastated because you weren’t, iyswim.
In truth every affair is different, it is naive to think otherwise. And it is perfectly possible to acknowledge that life is rarely black and white while still having experienced the wrong thing.
I grew up in a bit of a strange town where it was a very close-nit community and affairs were rife. Looking back I remember several couples who all had affairs, ultimately left their partners and moved straight in with one another, kids and all and they all continued to move in the same social circles as if it had always been this way. And decades on all those couples who got together as the result of the affairs are still married to one another and have close relationships with their children and the children (who are now adults) also still have close relationships with the incoming partners. I don’t understand it but it worked for them.
Conversely the dad of a school friend had an affair for the duration of the time we were in school, to the extent the OW would ring the house to speak to him and the kids both knew who she was. There was no question that he was not well thought of by all concerned. Friend’s mum stayed with him until her youngest left school and then she divorced him and he moved straight in with OW. The relationship lasted for six months and he then decided he wanted his wife back and still does years down the line.
And there also comes a point where a betrayed partner needs to move on, for their own sake. I have known people whose partners have had affairs go on to be the ones who were responsible for the most damage to the children, by turning them against their other parent, demanding loyalty to them because of what the other person has done, and ultimately that has caused much resentment and in some cases even the breakdown of the relationship with the children.
The cheating partner is responsible for the affair but the aftermath can be just as much the responsibility of the cheated-on partner.
And no, I don’t believe it’s about the children needing to know. I get that the children may find out but there’s a difference between that and turning the children against their other parent...