Can be Kurt having a lot of sex with different people, or having had sex with one person before, or continually hooking up with one person...
My only request is that the sex was consensual, and Kurt has had sex with more than one person. It can also be gen where sex is only mentioned. I don't mind if Kurt is in a relationship with one of the boys but has had sex with one of the others. I also don't mind if Kurt is in a relationship w/ one of the boys and has had sex with an OC. The fic can also be about something other than Kurt's sex life as long as it includes the above.
Tl;dr - Kurt has had sex with more than one person.