AceShowbiz -

Katy Perry and John Mayer reportedly called it quits again for the second time since they began dating in summer 2012. "It's sad," a source close to the couple confirmed the breakup. "It's not over until it's over. You have to see how things play out."

"She's leaving the window open. They have both been so focused on work," said another source, blaming the split on the couple's busy schedule. Indeed, Perry has been busy recording her third studio album in Los Angeles, while Mayer is preparing for upcoming tour dates.

They were first linked last June before splitting for the first time in August. The duo reconciled in September and this time they seemed to be growing more serious as Mayer spent Christmas together with Perry's family and attended several A-list events as a couple. Last month, Mayer presented Perry with a heart-shaped ruby ring which later sparked engagement rumors.

Back in February, Mayer told CBS in an interview, "I don't feel like I'm in a celebrity relationship. For the first time in my life I don't feel like I'm in a celebrity relationship. I know it is high profile. It's hard to explain... For me it feels like something that's very human."

In the interview, Mayer also admitted he had thought about marrying Perry in the future. "Of course," he said. "I mean, I'm still the kid from Connecticut. That's what you do (get married)."