Blaine POV. Kurt and Blaine are friends throughout the fic. I think Kurt is attending Dalton, but he could be just visiting. Anyway, Karofsky shows up drunk, in the parking lot and grabs Kurt by the arm and has him hemmed in by a car. Blaine calls the police, but he has to intervene before they get there (saying something to the effect of, "I can't wait, he'll hurt him," or the like). Blaine tries to get him off, both Kurt and Blaine are hurt (I think Kurt has a sprained or fractured wrist?). At the hospital, I think, is when Blaine admits wanting to be with Kurt (but once again, not positive).
Hopefully this isn't too vague! I'd love to be able to find this story.
It appears, right after posting this, I managed to find it. It IS one of rainjoy's fics - Confidences, in fact. Links for downloading in comments :D