I read a story a while ago, it was a kurtbastian story where I'm pretty sure they were engaged to be married, but Kurt was worried that he wouldn't be enough for Sebastian and figured he'd kind of "control it if it's going to happen anyway"; so he bought a guy home (from his work I think) for Sebastian but Sebastian misunderstood and thought Kurt wanted a threesome and called him kinky - and Kurt found that he liked the threesomes anyway but I think he was still insecure. I'm not sure if it was Kurt or Sebastian but one of them wanted to keep having the same guy round.
When Sebastian found out he was really angry and I think he said something about rape and that it was really insulting to him that Kurt thought like that - or something along those lines. I don't remember much else, but that's the general gist!
I would really appreciate it if anybody knows where to find this, being looking for awhile!
Thanks in advance!