Miley Cyrus & Justin Gaston Call It Quits

LOS ANGELES, Calif. -- Miley Cyrus has reportedly broken up with boyfriend Justin Gaston.

The 16-year-old pop star and the 20-year-old model had been dating for nearly nine months.

The "Hannah Montana" star reportedly called things off last week, as she was preparing to head to Georgia to film her new movie, "The Last Song."

"They have been having trouble for a while," the source told Us Weekly. "It's been hard for a long time since Miley has been working so much and traveling a lot."

However, distance may not have been the only factor behind the breakup.

Miley has recently been spending time with her ex, Nick Jonas, which a friend of Justin's said put some strain on the relationship.

"She obviously has been hanging out with Nick again a lot and Justin was cool with it at first - as long as it was just a cool friendly thing," a friend of Justin's told E! News. "She didn't cheat, but I guess Nick was trying to get her back the whole time."

Over the weekend, Miley hit up her Twitter page to Tweet about spending time with Nick.

"i'm in a dark theater 'writing' a song with nick j who is rockin a faded egg plant [sic] shirt!" she wrote.

In a new interview with teen magazine Twist, Nick confirmed a duet with his ex-girlfriend on the Jonas Brother's new song, "Before The Storm."

"There's two versions of the song basically, one that was written just for our record that we sang originally. And then I played it for Miley and we realized that if we just changed the lyrics a bit, we could make it more of our story, kind of share that side of us, and it could be great. So, we did," Nick told Twist. "She came in and she and I sat down at the piano and just worked on lyrics a bit, tweaked it up, and it turned out great!"

Since leaving for Georgia, Miley has posted several Tweets referencing the distance between herself and her loved ones.

"why does saying good-bye hurt so much?" she wrote on June 7. "I'm just to [sic] far from where you are, i wanna go home."