When Jennifer Lopez and Ben Affleck arrived at Beverly Hills' hip Matsuhisa restaurant at 8:30 p.m. on Jan 20, there was none of the usual kissing and laughter. Nor was there anger or yelling. Just the sober countenances of two people heavy with their own history and, once again, with issues to discuss: Say, his much publicized night of partying on Jan. 10 with Matt Damon and a bevy of female fans at a nightclub in Berlin, where he was promoting his recent thriller Paycheck, or, the same weekend, her equally ballyhooed evening dancing into the wee hours at the Miami Beach club Prive with ex-flame Sean "P. Diddy" Combs. During their hour-long Matsuhisa dinner, "they looked serious," says a witness. More than serious, actually. "He looked sad," notes the source. "She reached out to touch his head, like, trying to kiss him. And they gave each other a little kiss. But he really wasn't reacting to her. It seemed like something was wrong."

It was. Before the day was done, the caroming Bentley known as Bennifer – the passionate public embraces, the lavish spending sprees, the night he spent cavorting with strippers in Vancouver last summer and the stunning cancellation of the $2 million wedding last September that left her, according to a mutual friend, "hysterical and very deeply depressed" – had finally skidded to a halt. Two days later – and two years after they met on the set of their disastrous comedy Gigli – her rep announced that Lopez "has ended her engagement to Ben Affleck." And just like that, the couple-that-could faced the fact that they couldn't – and pretty much everyone close to them heaved a sigh of relief. "The relationship was a slow death," says a source close to them both. "It was a long goodbye."

So what finally took them from 6.1-karat Harry Winston engagement bling to bust? By all accounts, nothing as interesting as the rumor of a renewed romance with P. Diddy. "We're friends," says the rap mogul, 34, who has a son with his girlfriend, Kim Porter, 33. Adds a P. Diddy source: "There's nothing going on."

PEOPLE.com Photo Gallery: Bennifer: The Way They Were