The 31-year-old actress - who has six-year-old daughter Matilda with the late actor, who died from an accidental overdose of prescription drugs a few months after their break-up - admitted while "straight men across the board" hate her cropped locks, she keeps the style because the 'Brokeback Mountain' actor "really loved it".
She explained: "I feel like myself with short hair. And it's been a really long time since I had long hair, five years. Of course, the only people who like it are gay men and my girlfriends. Straight men across the board are not into this hair!
"I cut it for the one straight man who has ever liked short hair and I wear it in memorial of somebody who really loved it."
The 'My Week With Marilyn' star admitted she finds it "remarkable" that the couple's daughter still goes about life with "gusto and excitement", as she has a "mishap" every day of her life.
Michelle added to Britain's Elle magazine: "She likes everything girlie, but she'll climb a tree, play soccer. She has bruises up and down her leg. You know what I find so remarkable about her, and kids, is that every single day she goes to the playground.
"And every single day there's a mishap, an accident, a fall, there's a bruise, there's a cut, there's a scrape. But the next day she goes back out there with the same gusto and excitement."