Your two sides of whether to tell W about the other couple both involve what she's going to think: either feel validated or else to teach her that you were right about other people having problems. Both of these are looking at the wrong person in the equation. You can't control what she thinks and you shouldn't try. If these were good friends of hers as well as yours, and if she's on speaking terms with you, and you're sharing a conversation, then it makes sense to share the news. She'll feel what she feels, but it's a fact about some people she cares about, so withholding the information seems like the less good option. I wouldn't make a special call about it though. My two cents.
My other two: You have no idea what went on in the other relationship, even if the H told you his perception. The EA may have been preceded by years of the wife asking and begging for what she needed and having that fall on deaf ears. Or she got hormones at 40 and went nutso. You don't know, W doesn't know. In spite of the marked similarities between many of us DB'ers situations, it is an overgeneralization to suspect that the same thing is happening. Relationships are extremely complicated - the preferences and needs and communication abilities, emotional health, baggage from childhood, financial and child stresses, all combine in different ways.
Adinva 51, S20, S18 M24 total 6/15/11-12/1/12 From IDLY to H moving out 9/15/15-3/7/17 From negotiating SA to final D at age 50 5/8/17-now: New relationship with an old friend __ Happiness is a warm puppy.