Selena Gomez and Justin Bieber reportedly had major trust issues.
The 20-year-old actress-turned-singer allegedly dumped the Baby hitmaker last week because she couldn't trust him when they weren't together.
A source told People magazine: "She broke up with him about a week ago.
"With them being apart so much it got complicated. She had some trust issues. It's not easy, but the relationship needed to end."
Gomez and Bieber went public with their relationship in February 2011.
News of the couple's split broke on Friday night, just hours after Gomez posted a picture on twitter of a photograph of Bieber with Hungarian Victoria's Secret model Barbara Palvin in the background.
The Canadian pop star, 18, was spotted on a date with the 19-year-old model in New York earlier this week.
The pair - who met when Bieber performed at the Victoria's Secret show in the city on Wednesday - went to see the Lion King on Broadway.
The break-up is surprising because Bieber recently revealed he was proud to have Gomez by his side.
"I never make [Selena] separate from me because I don't want her to ever feel like I'm ashamed of her, because I feel like a lot of guys do that, especially in the business," he said.
"They don't want to be seen with the girl, so they'll make them ride in separate cars. They'll do that 'get away' stuff. [Selena and I] get away together."