Yes, I was cheated on before and I was very hurt. I still didn't think it was the girl's fault even though she knew about me. It was my boyfriend's fault completely. And I still today find it strange that she contacted me and told me about it (they had already ended it by that time, and my boyfriend had gone back to being faithful). It messed up my relationship with my boyfriend - we broke up for a few weeks, and after that I liked him a little bit less. I also had to be bashed by almost everyone I knew because of my choice, and defending why I wanted to stay in a good relationship.
As for the topic of the thread - it's not a "current" thing, we said good bye three days ago and I don't expect to see him again. He did however track me down on facebook which confuses me, because I can know easily contact his wife if I wish to. If I was married I would probably ask my husband who their new facebook friends are and how he knows them. It would be obvious from my profile (age/ethnicity/profession etc) that I don't know him in a way that could be expected and considered normal (i.e everything about us is quite different).
Anyway - I don't know why they're married, how long they've been married or if they really are in love. I don't know if I should assume that they got married because they've found the love of their lives, but the thread seems to think that is mandatory to make that assumption of all marriages and treat all married people as such. I simply don't know their circumstances. But he does, so he should be responsible over his choices.