Cool, I get you. Thinking on rules: I'm not sure if they're moves in the conventional sense or what. Your guy is essentially trying to end up with a move that says, "When you have sex with someone, set your Hx with them to +1, and their Hx with you to +1. Both of you mark experience." That seems to me like a pretty obvious attempt to game the system, you know? It kind of grinds my gears a little bit to think about it.
If that's true, and you allow it, the guy's basically going to be fucking PCs like bunnies. When someone's Hx hits +4 and gets reset, it's because the character has transcended some level of "knowing someone". So what are they learning? That this guy is a nympho? And on top of that, if he's spending so much time in the sack, what's going on around him that he's missing, or what is he spreading around? (Hard move time?) He might just end up with enough rope to hang himself.