After dating on and off since last summer, John Mayer and Katy Perry have broken up again, People reports. "It's sad," a source told Us Weekly. "It's not over until it's over. You have to see how things play out." In what is becoming the de facto Hollywood response, another source blamed the couple's busy schedules, saying, "She's leaving the window open. They have both been so focused on work." Katy Perry and John Mayer First spotted together last June, John and Katy called it quits back in August. That was short-lived, however, as the duo were seen smooching it up at awards shows and restaurants around Los Angeles the next month. Just last month, the seemingly happy couple was spotted together at the Grammys, with Perry even revealing to our own Sway that her "boyfriend" introduced her to the smooth sounds of Miguel. Mayer has left a slew of starlets in his wake in the past, including very public re