Michelle Williams talks death of Heath Ledger

Michelle Williams opens up about the death of Heath Ledger.

Williams and Ledger split in September 2007 after three years together. The couple's daughter, Matilda, is 5.

"In a strange way, I miss that year, because all those possibilities that existed then are gone," Williams, 30, tells Nightline.

"It didn't seem unlikely to me that he could walk through a door or could appear behind a bush.

"It was a year of very magical thinking, and in some ways I'm sad to be moving further and further away from it."

"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.'"