Caroline/Rebekah
Long story short, we thought there was a cure. Kol was trying to stop us from finding it. Klaus wanted to handle it but Elena and her brother decided to kill him instead.
Klaus wanted to know about the 5, they were hunters that could lead us to the cure. They needed the sword and I knew where it was. After I told them, Klaus was coming to dagger me before I showed up here.
Alaric killed my brother. No matter what he's done he's still my brother and I love him. I was heartbroken and I wanted Alaric dead. I couldn't do that without going through Elena.
I may have been the only one, but that didn't stop your friends from using me and betraying my trust.