Iwould be absolutely furious if someone told me, without being specifically asked, about anything that my partner had done. I would think it was none of their business. What happens in other people's relationships is up to them, not anybody else. We have known MANY people who have strayed in their relationships. They are normal, everyday couples leading their own lives in whatever fashion they chose. I would never say a word - it is none of my business how they chose to conduct their private lives. To be honest, I am not that interested, per se. I have been told a few things involving other people's relationships that I just know that the local busybodies would LOVE to get their hands on. I say nothing - no-one else's bloody business.
To be honest, if a bunch of busybody, know-it-all mothers with an agenda to save their world from infidelity came marching up with a self-satisfied grin and started telling me stuff I would probably punch them on the nose. Go and take their meddling, moralising, self-righteous agendas somewhere else, thank you very much.
This idea that everybody is living in a kind of 1950s Britain with 2.2 children and roses round a picket fence is just so naive. Apart from anything, look at the divorce rate.
My philosophy is to never say anything to anyone that would upset them - unless they had specifically asked me a question and I was sure they wanted the complete truth.
There are as many different types of relationship as their are people in them. Sometimes people chose to turn a blind eye, other times people want to live in a state of blissful ignorance, othertimes the truth is too difficult to deal with, yet again some couples have different ways of living. All are within the law and all are up to the people in them and no-one else.
More harm than good comes from meddling in other people's lives and "telling tales" is nearly always done for one's own agenda and to feel smug - it is not done to do a favour to anyone, and it doesn't.
You are all being so naive - look at all those married people dating sites - there are thousands of people on them - who do you think they are all? It clearly fulfils a need of some sort and a moral crusade against it is not going to save the world, however much the bible bashers and fundamentalists would want to.