Life & Style can exclusively reveal that the main reason for their breakup is that Ian wanted to get married and she just wasn't ready.
"He was starting to talk marriage and she is just getting started on her career," a source close to the actress tells Life & Style.
Their 10-year age difference played a major role — at 34, it's natural for Ian to want to settle down.
"She loves him, and they still talk every day, but she is just not ready to make that huge commitment yet," the insider reveals, adding, "Maybe in 10 years."
NEWS: Vampire Diaries' Nina Dobrev and Ian Somerhalder Split
We doubt Ian wants to wait until he's 44!
And it seems he's cryptically addressed their parting on Twitter today.
As Life & Style reported, the Vampire Diaries split after dating for three years. The pair met on the set of the hit CW show in 2009.
"I didn’t want to be dating one of my co-stars — my goal on the show was to be professional," she's said. "But sometimes you can’t help who you have a connection with, and you can only fight it for so long — which I did for a really, really long time.”
In late April, the brunette beauty enjoyed an all-girls vacation with the newly single Julianne Hough in Miami. The Safe Haven starlet, 24, recently ended her two-year romance with Ryan Seacrest, who is 14 years her senior.
At least these BFFs have each other to lean on!