I love "when did you know" stories.
I'm not perennially single because I'm repulsed by monogamy. On the contrary: I'm fascinated by it. If you're with somebody you want to be with forever, I want all the particulars. It doesn't matter if you're freshly engaged, newly wed, celebrating several anniversaries or cheerfully picking out side-by-side graves for your imminent deaths. I want to know how and where and why and when you went, "This person, right here. These genitals, for life."
Seriously, if you're one of those "When Harry Met Sally"-couch couples in any phase of your relationship, I want to hear about it in excruciating, forensic detail. I'm particularly obsessed with that watershed moment of knowing it was It. You know, the one you tell your grandkids about after one of you kicks it, and before the other one goes shortly after (of a broken heart, or mourning-based hooker-sex coronary).