It's been almost six months since Russell Brand filed for divorce from Katy Perry and the pop star has largely been quiet on why things didn't work out.

Until now.

In her new movie Part of Me, Perry, 27, pulls back the curtain to discuss why her marriage with Brand, 37, fell apart.

The biggest strain on their relationship, she reveals, was her busy touring schedule. As scenes in the movie show, Perry used days off from her grueling world tour to take side trips to see Brand. Yet the time apart still took its toll.

In one scene, Perry is seen sobbing uncontrollably backstage – minutes before show time. Eventually, she rallies. "Start time," she says before hitting the stage.

PHOTOS: Celebrity Couples: From Denial To Breakups

Perry also hints that her rocketing music career was a source of tension between her and Brand.

"I thought to myself, 'When I find that person that's going to be my life partner, I won't ever have to choose [between the partner and my career] … they won't be threatened or have weird motives," Perry says. "Then I started to realize, that's not true. That fairytale I had is not true for me right now."

The pop star says she did everything she could to save her marriage. "I have that same belief system with everything, from career to my life to my personal life, everything. And I will do everything it takes to not fail. And I did everything it took but it still failed."