They are both best friends with Caroline. Bonnie turned her back on Elena after her grandmother died, blaming
He chose to save Bonnie's life, knowing that it meant he wouldn't see Elena for decades. Their relationship was much more open and down-to-earth than what Bonnie had with Elena growing up.
Bonnie ended up finally taking control of her witch powers in the finale, saving Mystic Falls and breaking the curse keeping Elena asleep without having to die in the process.
Bonnie is slightly more evil than her grandmother, Sheila Bennett because she (to get revenge) would be evil. This is seen several times as she and Damon go from enemies to best friends while trapped in Kai's world.
The Crow is an animal introduced in Pilot, that would later reappear in I Was Feeling Epic. Damon compelled the crow to spy on people for him, particularly Elena, and it first bumped into Bonnie's car during a ride with Elena.
Bonnie is, in fact, possessed by the soul of one of the children killed by William Afton, which explains his temperamental and evil behavior.
They eventually rekindle their relationship, Elena takes the cure that Bonnie gave Damon. At Alaric's wedding, Kai ruins their wedding and casts a sleeping spell on Elena, linking her life to Bonnie's. She makes a sacrifice to let Bonnie live out her life until it is her turn.
Bonnie was stronger than Elena and Caroline.
Aside from caring about his younger brother Stefan, Damon has strong feelings for both Elena and Bonnie, though very different in nature. Damon gives Elena more attention because he sees her as a prize to be won, but he still happens to also love Bonnie.
Here's how it went down: Kai — who killed himself with Lily's blood in his system, thus becoming a heretic — put a spell on Elena, linking her to Bonnie; as long as Bonnie lived, Elena would remain in a sleep-like trance.
Following Stefan's death, Elena wakes up in the Salvatore mansion to find Bonnie standing over her. Bonnie's alive and managed to figure out a loophole to break the spell.
They have known each other since childhood and became close friends. They are both best friends with Caroline. Bonnie turned her back on Elena after her grandmother died, blaming Damon and Stefan and not wanting Elena to choose between her and them.
Last night, Vampire Diaries fans watched as Elena Gilbert was put into a magical coma when Kai linked her life to Bonnie's. So as long as Bonnie is alive, Elena can't be, which means that Elena went into a 60-plus year sleep in order to allow her best friend to attempt to find happiness.
After he tells her the truth, they mutually decide to end their relationship as they realize they have too much control over each other. However they end up sleeping together. But after that, Elena tells Damon that he has to let her go until they can figure things out.
Not only that, but Damon Salvatore was nothing but cruel to Elena, her friends, and family since the start of the show. He was responsible for killing her brother, placed her in harm's way multiple times to get Katherine back, and tormented her friends when he rejected her. The relationship was way too co-dependent.
Bon Bon (Bonnie)
While Damon has plenty of insulting nicknames for her as well, "Bon Bon" is used to exemplify their closeness.
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.
I Alone (The Vampire Diaries)
Damon is successful in relieving Bonnie of her Huntress side. Damon later calls Bonnie and she jokes with him, but all is forgiven between them.
Bonnie and Elena are much closer, and Caroline is often seen pursuing a separate life from her friends. Bonnie never viewed Elena competitively and supported her friend through her grief. Her friendship with Elena is much stronger than her relationship with Caroline in Season 1, who is more of a frenemy than a bestie.
Caroline is actually Stronger, but Elena was trained to kill vampires as a human. They both fought when Elena had her humanity off and she almost killed Caroline.
Then, upon their release, Damon was faced with an unimaginable decision: save Bonnie and lose Elena for the next 60 years or let Bonnie die and get the love of his life back. In the end, Damon chose Bonnie and that cemented Bamon's friendship as one of our favorite dynamics on the show.
Casting. On January 26, 2017, it was announced that Nina Dobrev would return as Elena Gilbert in the series finale. At the end of the episode, "It's Been a Hell of a Ride" on February 24, 2017, it was revealed that Dobrev would reprise her role of Katherine Pierce as well.
As to the reasoning behind the change in her appearance, fans suggest that Nina wanted to be seen as a more mature star -- so pursued some facial modifications.
A spell cast by villain Kai linked the two ladies together and put Elena in a deep sleep that will remain in effect for as long as Bonnie's still alive, meaning the door is still open for Dobrev to come back to the show one day.