Its written during Klaine's first fight on Glee, where Blaine accuses Kurt of being just like Karofsky. And Kurt takes it somewhat seriously, and decides that Blaine is right. I think he kind of cuts off all ties with Blaine because if he's like Karofsky then no one should have to put up with him. I'm not even certain! but Blaine goes looking for Kurt and they sort their relationship out on the stairs to Kurt's bedroom.
I hope someone can take this request and recognize the story. I'm sorry for being so vague; I read way too much and can never remember exact details of any specific fic.