Is John Mayer Playing Doubles?

Just who is John Mayer's girlfriend? The curly-tressed singer has been romantically linked to actress Minka Kelly, but last week, OK! spies spotted Jessica Simpson's former squeeze getting awfully friendly with blonde stunner Cameron Diaz at NYC's Goldbar in SoHo. Only a few months ago, the pair had heated up the Big Apple together while Cam was in town filming What Happens in Vegas. So could the two be reuniting for a winter wonderland?

Well... Don't assume anything just yet, as John was back with Friday Night Lights star Minka on Monday night. The two partied together with friends and danced all night at NYC hotspot Butter. "They looked really cute together and were having so much fun," a clubgoer tells OK! "Minka even was laughing as John really got down."

So who truly has John's heart? "He is friends with Cameron," a pal of the singer reveals to OK!. "But Minka is definitely his girl."