I know of a few, both the one that left and the one that got left. I am late 50s so many relationships have come and gone around me in that time.
I haven't cheated and I haven't been cheated on as far as I know. Oh apart from once when I was about 20 but that was not very significant a relationship and meh, we broke up and everyone moved on. No idea where he is or what he is doing. Hope he's well.
Of the people I know:
1 is settled happily with his AP. Have been married for 10 ish years. They have 2 dc. The ex met someone new a couple of years after. They too seem very settled. Afaik no more dc. They get on with their exes - not as in they holiday together but they catch up when they see each other at events and there is no animosity.
1 was left by their partner who moved abroad with their AP. I know ex and AP are still together but no idea what the state of anything is. My friend is very happy with their current dh. They openly say they are much happier and they and their ex should have split years ago but it needed something to push them and the affair was it. It was not nice but they are almost grateful as they are in a much better place now.
Another couple split after an affair. The affair lasted a good few years but they drifted apart. The left partner dates occasionally but can't be arsed to be in anything serious. Says they prefer living on their own. Big social group. I'm pretty sure there isn't much contact between the exes but no negative slagging off. Just disinterest it seems.
I know a couple more but you get the idea. They are all different but most seem to view it as just part of life's journey and after the initial turmoil, are really very content and stable. And happy. I think that is the crux of it. That they are all really settled and content people tend not to harbour anger. They understand that people do shit but that doesn't make them shit and there were reasons. And they prefer their lives now so how can you regret something if you are happy now as you wouldn't be in your current position had it not happened.
That's why I started this thread as the people irl I know are not a reflection of the visceral hate I read here. They just seem grown up about things. But then maybe an online forum in more likely to attract people with strong negative opinions. They do say that people are far more likely to leave review on stars if they want to moan that to praise.