The romantic relationship between the witch, Bonnie Bennett and the vampire, Enzo St. John.
Their relationship began in Total Eclipse of the Heart, when Enzo, who was working with Damon to track down the remaining Augustine members, decided that the best way to get Bonnie to help them find Wes was to threaten her boyfriend, Jeremy, with death. This set their relationship off to a rocky and antagonistic start, but they were ultimately able to set aside their dislike of each other to focus on bringing Enzo and many of Bonnie's friends back from the Other Side before its collapse.
In Season Seven, we see the pair in a romantic relationship, but in a flash forward, after Bonnie gets in trouble with the Armory, three years ago, and Enzo stepped up to keep them away from her. Enzo moves Bonnie up in a cabin, and over the years the two began to grow close. Two years later, after their romantic feelings had build up, the two started a romantic relationship and fell in love. After dating for three years, they have been separated due to the Armory's Monster mentally incapacitating him to do the creature's biding (along with Bonnie and Enzo's best friend, Damon). Bonnie, along with their friends, have tried to find and save Enzo and Damon from their mental hijacking by the Armory's unknown and mysterious creature. They are offcially reunited in Coming Home Was a Mistake, after Bonnie managed to get Enzo's humanity back on.
They are known as "Bonenzo" or "Benzo" (unofficially) by fans.