Credit: Dan MacMedan/

Nearly three years after Heath Ledger died of an accidental drug overdose, Michelle Williams is finally opening up about her former boyfriend (and father to Matilda, 5).

"In a strange way, I miss that year, because all those possibilities that existed then are gone," Williams, 30, tells Nightline of the 12 months that followed Ledger's death.

To cope with the loss, Williams began reading The Year of Magical Thinking by Joan Didion.

"It didn't seem unlikely to me that he could walk through a door or could appear behind a bush," Williams says. "It was a year of very magical thinking, and in some ways I'm sad to be moving further and further away from it."

Williams, who began a three-year relationship with Ledger after costarring in Brokeback Mountain, says she can "understand" why people "relate" to her tragedy -- but she still has difficulty wrapping her head around the situation.

"I've found meanings around the circumstance, but the actual event itself still doesn't..." she says before trailing off. "I can't find a meaning for it. I can find meanings in things and people and relationships that have sprung up, and friendships that have strengthened. I can find a lot of meaning in that, but not in why."

"I know I got kind of obsessed with that for awhile, the before and after. A lot of things died," Williams says as she fights back tears. "There's a line from a book that gave me so much comfort and it said, 'When you've truly lost everything, then at least you can become rich in loss.'"

These days, Williams is back to her smiley self -- especially when probed about her reported relationship with her Blue Valentine costar Ryan Gosling.

"She's like Brigitte Bardot meets Clint Eastwood. She's like a sexy cowboy or something," Gosling gushes of the single mom. "Creatively, we are doing it. Creatively."

When asked if they were ever romantically involved, the actor -- who is currently linked to Blake Lively -- clams up. "No, we're professionals," he insists.

Adds Williams: "He looks like he's lying, but he's not!"