The off-and-on couple had been together (this time) for about two months, having reconciled during a break from her current tour.
"So, for those few months they had a great time, pretending that it would last — and of course it didn't," a source told Radar Online. "The reason they have split in the past is because Katy gets busy. John can't handle the lack of attention, and she can't handle the trust issues she has when she's so far away."
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John and Katy first got together in 2012 after her divorce from Russell Brand and, it seems, they break up and get back together about as often as the weather changes.
"The fact that he does not have anything major going on with his career is really starting to take a toll on their relationship," Radar reports. "Katy is at an all-time high. She is starting to give in to what everyone around her is saying, that maybe she is too good for him."
During a relationship hiatus, Katy also dated music producer and DJ Diplo.
In an interview with Billboard in January, Katy spoke about her high-profile love life, saying "there is no handbook for love."
She continued, "In all my relationships, I've learned how I have to be more careful and that it's not up for public consumption."