Sources told TMZ that the 46-year-old Musk decided the relationship "wasn't right" and the 31-year-old Heard agreed. So, they avoided an acrimonious split and realized that their relationship "just kind of fizzled out."
Sources linked to the couple told TMZ they still care about each other but decided splitting was for the best.
Heard started dating Musk early last year, after her divorce from Johnny Depp was finalized. During their relationship, Musk appeared on Heard's Instagram page, and he reportedly gave her a Tesla car to woo her.
Sources said their first relationship ended because of their conflicting schedules.
"The timing wasn't good for them," an insider told Us Weekly. "He's super busy and works all the time. Amber is filming [Aquaman] in Australia until October. She's in no position to settle with him. She feels her career is just starting."
Musk, the billionaire CEO of SpaceX and Tesla, has been married and divorced twice. He was married to Canadian author Justine Wilson from 2000 to 2008 and British actress Talulah Riley from 2010 to 2013. He shares custody of his five sons with Wilson.
"If I'm not in love, if I'm not with a long-term companion, I cannot be happy," Musk told Rolling Stone after the first break-up.
In that interview, Musk said he will "never be happy without having someone."
"Going to sleep alone kills me," Musk said. "It's not like I don't know what that feels like: Being in a big empty house, and the footsteps echoing through the hallway, no one there – and no one on the pillow next to you. F—. How do you make yourself happy in a situation like that?"
As for Heard, she was previously married to Depp for 15 months before a public divorce. She accused him of being abusive and she planned to donate her $7 million award to the ACLU and Children's Hospital Los Angeles. Heard did not make the donation right away, since the divorce had not been finalized, but in November 2016, E! News reported that Heard donated $350,000 to the ACLU days before the divorce was finalized.