The actors -- who began dating in July 2009 after meeting on the set of the thriller Case 39 -- displayed their mutual adoration at the Montblanc cocktail party hosted by Harvey and Bob Weinstein February 26.
"When they were in the VIP section, they were cute with one another," an eyewitness told UsMagazine.com. "Bradley seemed very attentive with her."
A devoted Zellweger even skipped the Golden Globes to be by Cooper's side after his father, Charles, passed away January 15.
"She tried to make it work, but in the end it was too hard," a Zellweger insider tells Us. "Her friends feel bad it ended, but she's okay."