Perry told People magazine her tour schedule was simply too much, and it caused her marriage to deteriorate.
"I will do everything it takes to not fail," said Perry. "And I did everything it took but it still failed."
Perry, 27, and Brand, 37, spilt up about six months ago. She told People she would use off days on her world tour for side trips to see her man, but the time apart took its toll.
She said she thought she would be able to have both a time-consuming career and a relationship with someone who "won't be threatened or have weird motives."
"Then I started to realize, that's not true," Perry conceded. "That fairytale I had is not true for me right now."