Jessica Simpson and John Mayer are "off" again - and this time maybe for good. "It has been rocky and it had been rocky, and it reached the end of the road," a source close to Mayer told People mag. "It is definitely over - the relationship has ended." On Simpson's side, the story's not so clear cut. "They broke up Sunday night, but who knows what the future will hold," says a source close to Simpson. "This is the twelfth time they've broken up. Their relationship is volatile. Last week they felt better than ever. This week, things are rocky. Who knows what the future will bring?" The couple announced their split last month, but reconciled shortly after. "They tried to make it work. They dated for a year," says the Mayer source, and who added that the pair's recent trip to Cabo was an attempt "to talk things over... Every relationship has its differences, but with Jessica and John those differences were starting to become more and more apparent."