Heath Ledger and Michelle Williams have split after three years together, a source confirms to PEOPLE.

“It was rocky for awhile,” says a source close to the couple. “They did what they could to make it work.”

The source says the split was amicable.

The pair, whowelcomed daughter Matilda in October 2005, met while they were filmingBrokeback Mountain in 2004.

Costars say the chemistry was obvious from the start. “I remember being in rehearsal, and the two of them had googly eyes with each other,” costarJake Gyllenhaal said of the couple. “There were sparks immediately,” added costar Anne Hathaway. “It was adorable.”

The Brooklyn-based duo welcomed their daughter during promotion for the film, with Ledger calling the formerDawson’s Creek starthe perfect mom.

But the rigorous schedule wasn’t easy. “We started promoting the movie about three weeks after [Matilda] was born, which was too soon,” she said in a 2006 interview. “I’m just learning lessons now, like learning how to be a working mom.”