We'll Always Have Bourbon Street

After Elena and Damon wake up and continue where they left off the night before, Stefan arrives to the Salvatore house and approaches Damon with the suspicion that Elena is sired to him. Stefan advises Damon to ask Elena to try to drink from a blood bag again and see if she can keep it down, since he believes the only reason she can only drink straight from a vein is because Damon told her so. He tries and discovers that not only can she keep the blood down, she enjoys it. Damon decides to help Stefan investigate the sire bond in New Orleans, Louisiana hoping to find a former flame of Damon's who was also sired to him. While the Salvatore brothers are out of town, Elena, Caroline and Bonnie share a girls night, but an argument quickly ensues when Caroline starts criticizing Damon. When Caroline gets angry at Elena's stubbornness and her obvious devotion to Damon, Elena reveals that she and Damon slept together, which leads to Caroline telling Elena that she is sired to Damon. Meanwhile, at Hayley's urging, Tyler confronts one of Klaus's hybrids, Kimberly, and the situation quickly escalates into violence when the hybrids start fighting over who takes the pack-leader role. Kimberly then captures Caroline to try to prove that she is the leader. Tyler and Elena save Caroline, causing the other hybrids (including Kimberly) to accept Tyler as their leader. While in New Orleans, a witch tells Damon that the only way to break a sire bond is by telling the sired vampire to forget they ever existed and move on with their life. The witch also reveals that a vampire only becomes sired to their maker when they have human feelings for their maker before they are turned. Damon knows he has to do the right thing with Elena and decides to tell her to move on, but when he approaches Elena with this final instruction, Elena realizes that he wants to break things off and tries to convince him that her feelings are as real as she believes they are, and that the sire bond only affects the way she acts. Also in the episode, we find out that Professor Shane is teaching Bonnie a type of magic called "expression," which the witch in New Orleans called more evil than dark magic; that other witches don't even call it magic at all.

Plot summary from Wikipedia (CC BY-SA 4.0). Source