Damon showed up at your door when you called him. He knew Stefan had been dating you for a while after the break up and his own subsequent getting together with Elena. What the elder Salvatore hadn't expected to occur was for Stefan to go ripper, turn his humanity off, and turn you into a vampire in the process.

"Can I come in?"

The raven haired vampire asked, for once not a single sarcastic or witty comment to be heard. His icy blue eyes showed nothing but concern for your well being. In his hand was a blood bag to allow you to complete your transition from human to vampire.