"They broke up in February," the insider tells Us, adding, "they still really care a lot about each other but it was impossible to remain a romantic relationship with the careers they have."
The two have remained amicable since the breakup. In April, Bush confirmed that her ex was okay following a scary Mt. Everest avalanche. "For all concerned, @danfredinburg & team are safe at Camp 1 on #Everest after the avalanche," she tweeted at the time. "Please keep the Sherpas in your prayers."
Us broke news back in April 2013 that Bush and the Google program manager, both 32, began dating. He's "super intelligent—and she really likes him," an insider told Us at the time. "She's mentioned wanting to marry him and I won't be surprised if she gets engaged!"
Bush kept the couple's romance quiet for the majority of their relationship, only stepping out as a couple publicly a few times. Last year, however, she gushed about Fredinburg after he came out to support her at the Do Something Awards in Hollywood.
"I usually shy away from personal stuff, but I'm feeling real emotional tonight...Hosting the @DoSomething Awards was a milestone for me," she wrote via Instagram on July 31, 2013. "And I wouldn't have been the same without this man by my side. Thank you, Dan, for loving my passion and my fight. Thank you for being the spark to my match."
Bush previously dated her One Tree Hill costar Austin Nichols on-and-off for six years until their split in February 2012. She's currently on location in Chicago filming the second season of the NBC drama Chicago P.D.