Is Jennifer Lopez cheating on her boy-toy with her ex-husband?

Word has it J. Lo left current beau Casper Smart at home in L.A. for her recent trip to New York -- where she met up with Marc Anthony.

According to a source, Anthony sneaked out after their secret rendezous and jumped into his waiting tour bus. "He came out really quickly, with his head down, like he didn’t want to be seen." JLo -- clad in thigh-high stiletto boots and a leopard-print micro-mini -- emerged soon after with a "smug grin on her face."

Casper, meanwhile, was home alone 3000 miles away with the couple’s recently adopted dog, Bear.