Hoping you can help me find a fic I read on AO3 (almost positive). It was a Kurt and Sebastian meet in collge fic. It's told in a flashback format with Kurt deciding on whether or not to buy a ring. Rachel is also shopping for jewelry because she is going/nominated for a Tony award.
They meet when Kurt has a college boyfriend and Sebastian tries to pick him up in front of Kurt (surprise, surprise). Sebastian is Kurt's roommate's friend or something like that. Kurt is dumped and sort of picks up Sebastian as a friend, they keep the canon snarky relationship. After a series of failed relationships, Kurt and Sebastian start a casual sexual relationship, at least on Kurt's end. Eventually Kurt realizes that they are boyfriends and buys Sebastian a ring to propose to him.
In the fic, Sebastian lets Kurt know that even though Kurt wants a fairytale romance, Kurt is sort of too self-involved to reciprocate romantic heartfelt gestures and that's why his (other) relationships never worked out. Also, when Kurt and Sebastian start their relationship, Kurt still sleeps with other people thinking that they have an open casual thing, but Sebastian never does.