A source tells E! News that the couple's relationship of nearly two years has hit a rough patch and a breakup may be imminent.
"Things are not going well at the moment," the insider says. "They are bickering and it's clear to the people around them that there is an irritation between them at the moment. It's hot and cold, but more cold than hot right now."
We're told that those close to J.Lo are not sure if it's going to last between the thrice-divorced mother of two and her choreographer beau and that Lopez, for one, "never thought it was going to be long-term."
Reps for Lopez and Smart have not responded to requests for comment.
Lopez, who separated from third husband Marc Anthony in July 2011, "was really drawn to Casper because he was so attentive to her when she split from Marc," the source continues. "She was lacking confidence at the time and he was the best medicine for her. He gave her back her confidence and made her feel special."
"Jennifer finds it difficult to be alone," the source adds. "She loves being in a relationship. She's the ultimate romantic. She wants to be in love. But she is also one of those women who is strong enough to walk away when it isn't right. "
Various reports have suggested that the reason they've lasted this long is that Lopez's twins, Max and Emme, really adore Smart, who met their mom when he worked as a backup dancer for her.
"He is certainly not the big love of her life—she knows that, he knows that," our source says. "If this relationship lasts it will be surprising to everyone."
For now, Lopez is back to work as a judge on American Idol, sharing the panel this year with Keith Urban and Harry Connick Jr.
While she and Smart were last photographed out in public on Sept. 21, he tweeted a pic, dated Sept. 26, of the two of them smiling by a fountain.
"My boo & I having a #datenight out on the town!! ;) @JLo," he wrote.