How does Santana actually know about Karofsky kissing Kurt? No one ever said anything about it during the Blaine, Kurt, Karofsky, and Santana confrontation. Both Blaine and Kurt were telling Karofsky that he needs to just give it up because he's a coward when it comes to the truth. They didn't actually say anything about the Kurtofsky kiss, unless maybe Kurt or Blaine told Santana about it, which i think is also unlikely.
