Get your tissues at the ready, another power-couple have reportedly split up. Jennifer Aniston and John Mayer are no more according to latest whispers.The couple got together earlier this year, and Jen has been following her rocker boyfriend like a lost puppydog. However, John has supposedly had enough and decided to call it quits.A source tells the Daily Mirror: "There's been a bit of tension for some time. They initially opted for a break, hoping a trial split might make them stronger. Sadly it doesn't seem to have worked."John took the decision to end things as he felt he just wasn't ready for the level of commitment that Jennifer deserved. Contrary to reports, Jen didn't want to have kids or marry this year, but she did want to set a timetable for their future together."Initially Jennifer was furious when he told her of his decision but now she's simply sad - not to mention a little heartbroken."And the source reveals that a reunion is unlikely.They add: "They have spoken on the phone since the split and are trying to remain on good terms. But unless John has a dramatic change of heart, it's unlikely they'll rekindle their romance."