It sounds like Taylor Swift was worried that Harry Styles didn't completely belong to her.

The two broke up earlier this month because Taylor was having a tough time trusting Harry, according to STAR, a British magazine. 

"Taylor’s trust issues contributed towards their argument," reveals a source. "She says she couldn’t cope with all the attention Harry gets from fans, and the fact he is a massive flirt with girls."

"She knew that if they were to spend huge amounts of time apart, trusting him to remain true to her would be pretty much impossible,” the insider continues. Yikes!

It sounds like the age difference made things difficult, too, as Taylor is 23, and Harry is only 18.

"She thinks he’s just too young to settle down and is having too much fun playing the field," says the source.

And the criticism from One Direction fans was apparently getting to her. 

"Taylor was also sick of getting nasty tweets from his fans about how they shouldn’t be together," continues the source. Why you gotta be so mean, 1D fans?

So Taylor was having worried about Harry staying faithful? Doesn't she know she's beautiful?

Source: STAR via Hollywood Life