Let's say, for example, that your spouse went to a concert - you didn't go, because you weren't interested. While there, your spouse got into a conversation with a member of the opposite sex. At some point, this person proposed sex with your spouse. Your spouse told the person, "No, I'm married." But the other person said that's OK, lets do it anyway. Your spouse may have thought the other person was good looking, but still turned down the proposition, and that was the end of that, and they never had contact again.
Now your spouse is feeling a bit guilty about having felt flattered about what happened. Would you want your spouse to tell you any of this? All of this? None of this?