I know I'm going to get flamed for this, but I was seeing a married man on an off for nearly a year. Not just sex, there was emotion involved too. I cut it off the first time as I knew it was wrong and then stupidly went back, following which there was talk about his situation maybe changing and us being together. It's become clear that this won't happen and he's withdrawing - and to be clear I'm not looking for sympathy - but if you were the spouse in this situation would you rather know or not, assuming they subsequently fully committed to you? I'm not going to say anything as it's not my place to do so and I knew what I was getting into. Sex was always safe so no worries re STIs etc. I think I'd rather know, but maybe others wouldn't if this was a one off mistake in a c. 30 year relationship?