Dishing exclusively to E! News, a source tells us that the 29-year-old pop star felt for a while that something wasn't quite right between them, that something was missing.
Perry knew that there were certain differences in their personalities and, deep down, she suspected that she and Mayer were not right for each other, the insider says.
But as tends to be the case, it took the Prism artist time to acknowledge her instincts and pull the trigger on their breakup, which she finally did just over a week ago.
E! News first reported that she and Mayer had split up after about a year and a half of dating off and on, and speculation immediately kicked into overdrive regarding the tipping point.
Perry, who's currently in Australia on a promo tour, had been having doubts and ignoring them, the source says, and so to have it all over with now has been a relief for her. She made the decision and it's been good for her—all in all, a positive move, and now she can get on with her life.
But what of reports that Mayer was engaging in his stories bad-boy behavior while he and Perry were a couple? Another source told us that a story about his supposed cheating involved a girl whom he was actually interacting with during one of his and Perry's off periods.
Meanwhile, the source who tells us that Perry is relieved also says that she didn't suspect Mayer of stepping out on her, that she just didn't think that way when it came to their relationship.