Kurt has a boypussy and he and Blaine are in a vaguely D/s relationship. They both get off on humiliating Kurt who has a safeword but has never used it. I remember that Blaine had been teasing Kurt all day and wouldn't let him come. They were going out with the rest of New Directions that night and Kurt soaked through his pants. Blaine came back from the bathroom and ND said they thought Kurt had an accident and he had run out crying. Blaine made an excuse that Kurt was on some kind of medicine that made him have accidents. Blaine goes out to the parking lot to find Kurt and he is fucking himself on the gear shifter in the Navigator. Blaine takes him home and fucks him.
Any help is very, very much appreciated! I hope I've done the tags correctly.
ETA: Found in comments!