Celebrities & Monogamy: Not a Match

Beautiful people. Exclusive parties. Free-flowing booze. Lavish homes, often with custom-made beds. Monogamy.

Which one of these doesn't belong?

Hollywood was created for hookups. If the tabloids and blogs are to be believed, the dynamics of the celebrity dating pool are akin to those of a high school cafeteria. (Pamela Anderson and Rick Solomon are splitting! Wait, now they're back together! No, now she's kissing Tommy Lee!)

And while some celebrity couples look like they only have eyes for each other — Brad and Angie, Tom and Katie — it seems natural that, in the land of surgically enhanced babes and treadmill-toned guys, some stars might want one partner to cuddle with in their multimillion-dollar mansions, and another to show off on the red carpet.

Tilda Swinton, the 47-year-old Oscar-nominated "Michael Clayton" actress, recently rolled up to the British Academy of Film and Television Arts awards ceremony with a man 18 years her junior, while her longtime partner, John Byrne, watched their children at home.

Byrne, 68, told London's Daily Mail that he and the actress live "amicably" in the same house, that they're "the best of chums" and that, "We love our children and our children love us. The rest is business."

Perhaps not all business. According to the New York Daily News, after the BAFTA awards, Swinton, Byrne and her younger man had a jolly old time at Swinton's home in Scotland.

ABCNEWS.com's repeated requests for comment from Swinton's publicist were not returned.

"Hanging around at fancy parties, seeing options. … When you have a lot of time and a lot of resources, you also have a lot of options that the rest of society might not have," said Los Angeles-based psychoanalyst and relationship specialist Bethany Marshall. "But you'd have to have a lot of fortitude to make an open relationship public."

Indeed, Swinton, a highly respected actress who's endured scant gossip through her two-decade-long career, has suddenly become a tabloid star. (A Gawker.com blog post about her Monday was headlined "Crazy Indie Actress in Crazy Indie Relationship.")

If Swinton is in an open relationship, she wouldn't be the only nonsingle star to break the bonds of monogamy and share her bed with someone other than her partner.

Jerry Hall put up with Mick Jagger's reportedly rampant infidelity throughout their nine-year marriage, until it was revealed that he had fathered a secret love child with Brazilian model Luciana Morad.

Vanessa Bryant stood by her NBA baller husband, Kobe, while he fought sexual assault charges, even after he admitted to having sexual relations with a young fan. (Of course, the $4 million, eight-carat, purple diamond ring he bought her might have helped.)

And most recently, a newly released sex tape features a man who appears to be Kiss frontman Gene Simmons in bed with an Australian model, though he has two children with his longtime partner and former Playboy playmate, Shannon Tweed.

"I can't believe that Ms. Swinton is the only person in Hollywood who might have more than one escort," said Dossie Easton, therapist, nonmonogamy advocate and co-author of "The Ethical Slut." "It's also true that these award shows have limited seating, and if you had five partners, they wouldn't let you bring them all, so you'd have to pick one," she quipped.

A nontraditional relationship isn't likely to hurt Swinton's public image. The actress isn't a huge name in the United States, and she has a reputation for making bold, quirky career choices.

"It's much the same as when Cynthia Nixon came out," E! online columnist Ted Casablanca said of the "Sex and the City" co-star revealing her homosexuality. "When a supporting star does something that is eyebrow raising, it has less of an effect as when a leading star does it. It's Tilda Swinton — no offense, but it's not exactly Julia Roberts going off with some other dude while Danny [husband Daniel Moder] is at home taking care of the kids."

And an open relationship need not be a tumultuous one. It's very possible that Swinton and Byrne can be "the best of chums," as he said, even if she's gallivanting around town with another man.

"We assume, if somebody has two partners, that they must be at each other's throats and competing, and that's not true at all. It's actually very rare. The reality is a lot easier than the fantasy," Easton said.

"This could just be a relationship of convenience. He could be as neutral about her having alliances with other men as he is about a business deal," Marshall added. "All relationships are arrangements. Some are sexual arrangements, some are marital arrangements, some are financial arrangements. And as long as the arrangements are agreed upon by both parties, that's all that matters."

But in a town where back-stabbing is sometimes a business necessity and image is everything, Casablanca predicts a thorny ending to Swinton's alleged three-pronged love story.

"It's like a threesome. Someone's not getting what they want," he said. "The person who is getting what they want is Tilda. And now that she's got her Oscar nomination, she's probably thinking about getting into foursomes."