"I have been cheated on," admits gorgeous Aussie actress Naomi Watts (search). "You always fear it. It's horrible."

Her revelations accompany the arrival of her latest film, "We Don't Live Here Anymore," (search) a twisted tale of suburban wife-swapping.

The 35-year-old -- who shot from obscurity to A-list status in 2001 with David Lynch's "Mulholland Drive" (search) and won an Oscar nomination this year for her role in "21 Grams" -- won't say who betrayed her.

But Watts did split with fellow Aussie actor Heath Ledger (search), who's 10 years her junior, in May. The couple had been off and on for nearly two years and had been spotted house-hunting together in L.A., and Ledger escorted Watts to the Oscars.

Neither has publicly commented on the break-up.

Yet the actress is fairly open about having had her heart broken, without naming names, of course.

"I've never been married," she says, "but I've been forced to face infidelity and been hurt by it."

In her new movie, Watts plays Edith Evans, a well-off yet unhappy housewife whose husband, Hank (Peter Krause), is serially unfaithful. Lonely and desperate, Edith embarks on a reckless love affair with her best friend's husband. Laura Dern and Mark Ruffalo play the other couple.

Watts says she really understood her character's suppressed rage.

"I know what it's like to bottle emotions; I've definitely been guilty of that at times," says Watts, who looks utterly composed in a low-cut, white silk dress.

"But I know if I keep my emotions in, I'll explode over the most ridiculous thing," she says. "Suddenly, it all comes bubbling out and I'll be completely irrational."

Watts decided to take the role of Edith after wrapping another hugely demanding film, playing opposite her "21 Grams" co-star Sean Penn (search) in "The Assassination of Richard Nixon."

She says the chance to play the emotionally repressed Edith was too much of a challenge to pass up.

"I always feel I'm boring audiences when I'm not doing anything, when I'm not emoting," she says. "Being still and passive is very scary to me. I always think it's not enough."

And though her character does some despicable things, Watts tried not to judge her.

"Rather than confront her husband about his infidelities, she turns a blind eye to it. And she decides the only way she can survive -- because there's no passion, truth, kindness or love left in the marriage -- is to jump into an affair. It's her cry for help."

The actress is fascinated by love, betrayal and why certain couples survive infidelity and others do not.

"I have married friends who have been through infidelity and gotten through it," she says. "I've had friends who've had the desire to be with someone else in an animal way, and I think that's completely human."

And even though Watts has been cheated on, she says it doesn't necessarily mean the end of a relationship.

"I love it when I hear someone say that they had that desire, and got honest with their partner and talked about it -- rather than the partner going, 'Damn you' and getting all jealous and reactive. In some cases, the partner has gone, 'OK, that hurts, but I do understand it.'"

Watts -- whose best friend, fellow Aussie Nicole Kidman (search), went through her own high-profile divorce -- says such honesty can even help revive a flagging relationship, because "the person becomes so much greater and so much sexier."

Watts may be in a bit of a romantic dry spell, but her career couldn't be more sastisfying.

She just finished shooting "The Ring 2," the sequel to her smash 2002 horror film. And she was handpicked by powerhouse "Lord of the Rings" director Peter Jackson to star in his remake of "King Kong," which began shooting this month in New Zealand.

"I've never been in a movie that has that kind of spectacle," she says excitedly. "What better person to do it than with Peter? It's a very simplistic story, even though it's a fantasy."

And, of course, there's another element -- her favorite.

"It's the unrequited love part of it that appeals to me."