Katy Perry and John Mayer split up because of her upcoming world tour.

The "Dark Horse" singer, 29, was reportedly dumped by the singer-songwriter, 32, because they were arguing a lot and she is "stressed" about her Prismatic concerts, which are scheduled to kick off in Belfast, Northern Ireland in early May and will see her travel across three continents until the end of the year.

"She's stressed about the tour, they've been fighting. It is probably for the best, because she is going to be on tour for forever. Of course this happens all the time, I can't keep track anymore. But for now they are done," a source said.

The duo, who released the romantic duet "Who You Love" in December, first began dating in summer 2012 and had an on/off relationship until things became serious between them last year, after Katy publicly admitted she was "still madly in love with him." A friend predicted they could reunite again, saying, "Not sure how long it will last this time but yes, it is off for now." But a third source said, "They've had rough patches, but this may be for good."