My first indication that KK might have slut tendencies happened when we were dating, near the transition from casual to steady relationship. We'd been planning a beach weekend, at the last minute I had to work, leaving KK and the group of friends on the outing, me stuck at work. In the days following that beach trip, things were strange on several fronts; KK was kind of stand-offish, and there were lots of rumor, innuendo, and such about KK's adventures that day on the beach...
I chose to deny it all. The story I was able to knit together was that KK had shared a ride with one of her girlfriends, her boyfriend, and two other guys, acquaintances. On the drive to the beach, KK apparently got finger-banged by both guys in the back seat. That wasn't the worst of it - I heard from two reliable sources that KK spent most of the day inside a tent the group had pitched on the beach, providing handjobs, blowjobs, and in at least two cases, full-on fucking (there were independent witnesses to both fuck sessions...)
I put it on myself at first, should'a been there, all that... then I blew it off, circling around it didn't really happen, just jealous gossip... that said, it never faded away, my thoughts about what a slut she could be, based on my own experience, and the rumors. It took much longer for me to come to grips with reality.