Yes, this letter seems a severe over-reaction, unless LW simply didn’t express herself well and this other couple was already exclusive or even engaged/married when her husband dated her. Or, she and husband were exclusive. Otherwise, to have expectations about your spouse’s/SO’s prior sexual history before you were an item seems misplaced.

Chiming in to say I agree with above. Why are you disgusted and upset? He dated someone in college and didn’t tell you about it till now. Did you think he was a virgin when you met? Is your reaction because of puritanical religion?

Was there some expectation of purity, like “You’re the only woman I’ve ever been with.”?

I’m not getting the furor from either spouse but I would understand disappointment from the omission for so long.

I understand the surprise. Less the “disgust”. You both react as if it was an affair, a stab in the back for both spouses. But this relationship took place before your both relationships, right? Nobody is entitled to be fully briefed about the romantic and sexual past of their partner. This is their privacy, their right. They hadn’t any duty of fidelity or transparency towards you at that time. And I think it is best not to dig too much in each other’s past.
Sure, it is strange to learn that a familiar friend is in fact an old date or an ex. I would be shaken too. I would like to learn a bit more given such a revelation : why the secrecy? How long did it last? Was it serious or just a try? What are they to each other now? How he feels now that the “secret” has been revealed? Then I would keep in perspective the fact that this is his romantic past pre-me, and let it go.
I think that this is stranger for the friend though. Usually, a close friend knows whom you are dating. And if he starts dating the same person, and doesn’t know that this is my ex, I would say it, I think (though I never found myself in that situation). But perhaps they weren’t that close at the time. Anyway, this is all related to private life and right to privacy, before the marriages or exclusive relationships. Respect it. Not such a big deal.

Yeah… the reactions of both the LW and the husband are pretty off the wall to me. And to most everybody else —- it seems.