Agree with Cogito and Leavenheath, I think those posters are really very insightful.
I call 'bullshit bingo' whenever I hear that "When a man marries his mistress it creates a vacancy". It doesn't. If you think about it, a man (or woman) who has ended their marriage does not do so lightly. Through selfishness or just a sense of decency and/or self-preservation, you don't just jump into matrimony again and not without giving it some real thought and consideration.
As a woman who was cheated on herself, I find some of the platitudes spouted extremely patronising and ill-considered. Above all, they are inaccurate and no kind of salve whatsoever. I just don't think it's helpful to fill people's head with this sort of stuff; "Don't worry, they'll get 'theirs' in the end", "They'll never be happy", "It's all built on a lie" and other assorted and completely unfounded statements.
What I've learned is that even the most uncharacteristic people have affairs. Many of those people are decent and whilst the affair behaviour is deplorable it doesn't change the essence of a person. It is always the 'fault' of the person who had the affair but given the destructive nature of entering into one and the huge risks and likelihood of getting caught, I doubt that it's something most people would do without seriously considering the implications of that. Some people, having considered, will still take that risk
You don't have to like or forgive a person who has cheated on you, you can even hate them if you want to but, there's one wisdom that strikes a chord with me along the lines of "If you seek revenge, dig TWO graves".