Once upon a time, I dated a Really Troubled Guy. And the Really Troubled Guy did a Very Bad Thing and then told me all about it. I went just about crazy with grief. I went so crazy with grief that I called up my dad to tell him all about it, and my dad's first response was not "Oh, what a Bad Thing!" but "And he TOLD you?"
This reminds me of the time my mentor told me about this Really Bad Thing she was doing. I went straight from her office to a pub, got drunk, and went to my then-boyfriend's apartment to cry. I had a key, and he found me on the bathroom floor crying and repeating "Why did she TELL me? Why did she TELL me?"
What a dramatic life I have had.
Anyway, the point is that people do a lot of Bad Things, and the world would be a better place if we all stopped telling the wrong people about the Bad Things that we do. Of course, it would be great if we didn't do the Bad Things at all, but once they're done, they're done. The only things we can do are make amends to the people hurt, if applicable, and to go to confession to a priest or, if not Catholic, to hired psychiatric help. The psychiatric help can at least help you to forgive yourself.
Of course, it's tricky when the person talking to the wrong people about the Bad Things doesn't perceive that these were Bad Things at all. For example, if you are dating a badly catechized cultural Catholic, he may let drop that he lost his virginity in high school to the blonde champion figure skater he'd loved all his life, and then moved in with his college girlfriend who wrote her Women's Studies thesis on Eastern sex manuals, but then they broke up, so he just played the field until he got tired of the drama, and now he's met you, and maybe it's time you took the relationship to the "next level".
By the way, whenever anyone talks to you about taking your relationship to "the next level", even if your heart is breaking, you must open your eyes very wide and ask, "Are you asking me to marry you?" This way the men of the world will stop with the "next level" nonsense. The human heart is not a video game.
Of course, another and wiser man will know that it is a bad idea to tell the new girl all about the old girls, especially if and when he very much wants to impress the new girl and not give her any excuse to dump him flat. In this situation, you should not ask him point blank about his other relationships. Well, obviously you need to know if he has ever been married, but intrusive questions about how many girls he has dated and what sexual things he has done are not wise. If this guy is a good guy and a committed Christian (or Jew or Muslim) who believes firmly in fidelity, the less you know about the details of his relationships with other women, the better. That he had them, okay. What they did, not so okay. Think of the poor women, their private lives now revealed to you.
The one exception to this rule is whether or not he has an internet porn addiction. A guy with an internet p*rn addiction, like the guy addicted to drink or drugs (and still using), is not eligible. It is easier to tell if a guy is an alcoholic than a compulsive user of p*rn, and how you can find out a guy is a compulsive user of p*rn without asking or snooping on his computer is a mystery to me. I suppose the best thing to do is engineer a conversation about p*rn, especially if there is a p*rn scandal in the news. And then, if he gets all self-righteous and excited about the subject and tells you there is no such thing as p*rn addiction and there is actually nothing wrong with p*rn using consenting adult actors, face the painful reality that Mr Perfect Until He Said That is a p*rn user.
I think the way I dealt with that was to say, "So, B.A., do you ever look at internet p*rn?" And B.A. said "No." End of story.
A more dramatic and amusing story is when some ex-flame of B.A.'s came by the Historical House for some outdoor Historical House event, and I scooted back into the Historical House like she was a rat infected with the bubonic plague. I stared out the window hissing and meowing to myself until I couldn't stand it anymore and called my friend Lily in Canada. We meowed and hissed together. And I learned from that event that although I don't mind that B.A. has ex-girlfriends (and even tried to get engaged to one once), I don't want to see them.
Lucky me, I don't have to see them. And every year they are more in the past anyway. And since everyone helps shape everyone else, I suppose I have a sort of grudging appreciation that, in ways either good or bad, they helped B.A. learn lessons about women, relationships and life, so that he is the great guy I met in 2008. I don't know the details, and I don't want to know, in part because it's not really any of my business. B.A.'s life was none of my business, and my life was none of his business, until October 2008. And my principal business, as his wife, is making sure that he is happy, healthy, well-fed and practicing his religion. If he does bad stuff, his confessors can sort him out.