Image caption Newt Gingrich and his now ex-wife, Marianne Gingrich, in happier times

Republican presidential candidate Newt Gingrich's ex-wife has said they divorced after she rejected his request for an "open marriage".

People in open marriages have told the BBC that if her version of events is true, the former House Speaker broached the subject the wrong way.

Several years after their wedding, Jenny Block realised that even though she loved her husband and wanted to be with him, she needed more.

Today, Ms Block, a writer, lives with Christopher in Dallas. Her girlfriend Jemma does not live with the couple - but spends a lot of time in the house.

"It's been me and my girlfriend and me and my husband, and the two of them are really good friends, but they're not sexually involved," says Ms Block, 41, author of Open: Love, Sex and Life in an Open Marriage.

"We're the most boring, regular, Scrabble and takeout Chinese on Saturday night kind of family.

"I have one other partner - that's the difference between our marriage and other marriages. No hanging naked from the chandelier. You couldn't detect anything if you came over for dinner."

'Callista doesn't care'

Image caption Jenny Block says the "Cinderella path" of monogamy was not for her

On Thursday, the already rollicking race for the Republican presidential nomination was shaken up by a lurid accusation of infidelity from the ex-wife of former House Speaker Newt Gingrich.

Mr Gingrich had previously been accused of cheating on Marianne Gingrich, his second wife.

But she told an interviewer that Mr Gingrich had asked "that I accept the fact that he has somebody else in his life" and also suggested that she share him with his mistress.

"I said to him, 'Newt, we've been married a long time.' And he said, 'yes, but you want me all to yourself. Callista doesn't care what I do,'" Marianne Gingrich told ABC News in an interview broadcast on Thursday. "He was asking to have an open marriage. And I refused."

Mr Gingrich has angrily denied his ex-wife's version of events.

But in any case, that 18-year marriage ended in divorce, and Mr Gingrich is now married to the former Callista Bisek, the alleged "somebody else" of Marianne Gingrich's version of events.

Polyamory versus swinging

In interviews, people in open marriages say that although it is not for everyone, it is absolutely possible for adults to be in committed, emotionally satisfying relationships with more than one person at a time.

Image caption "Everyone needs to be on the same page," says Tristan Taormino

The preferred term is polyamory, a word coined in the early 1990s in the US in part to distinguish from swinging, in which couples approach sex with other people as a joint endeavour, or arrangements in which partners are allowed to have sex with other people without romantic attachments.

"Polyamorous relationships tend to be ongoing, sustainable, emotionally bonded, committed relationships with more than one person, with the knowledge and consent of everyone involved," says Anita Wagner, who says she has been in polyamorous relationships on and off for the last 15 years.

"When it works, it's wonderful. It's an abundance of love and affection and experience."

The keys to a successful, happy polyamorous relationship are up-front consent and negotiation of ground rules and boundaries, say relationship counsellors, sex educators and polyamorous couples.

"That can range anywhere from 'you can only have sex when you go on business trips and you're out of the state', to 'you can have another girlfriend but I'm the primary partner, so I come first'," says Tristan Taormino, a sex educator, writer and feminist pornographer.

"It could be, 'I'm a gay bear leather guy, and you can't see any gay bear leather guys but me,'" says Ms Taormino, author of Opening Up: A Guide to Creating and Sustaining Open Relationships.

"It can get really down to specific minutiae like that, or it can be very broad. It really depends on the couple."

Odds of failure

Ideally, the polyamory discussion takes place in a monogamous relationship well before the start of an extramarital affair.

Picture your best friend, only you have a romantic relationship as well Jenny Block, Writer and polyamorist

"It would sound more like, 'I've been feeling like I've been wanting to open the marriage, can we talk about that,'" says Deborah Anapol, a San Francisco psychologist and relationship therapist who has been coaching polyamorous couples for three decades,

"If there's already a pre-existing relationship, that increases the odds of failure significantly."

Even couples who believe in polyamory in theory find it difficult to broach the subject.

"It takes a lot of courage to look someone you love in the eye and tell them that you fancy another person, even if you've agreed already that you're going to do this," says Ms Wagner.

"It's not something we're used to doing. We have no role models for this."

'Three-adult household'

Ms Block, 41, lives with her husband Christopher, a 47-year-old IT manager, and their teenage daughter. She describes Jemma, a 30-year-old copywriter, as one would a frequent houseguest and dear family friend.

Image caption Ms Wagner and her new husband Tim are not polyamorous - for now

"He is an excellent cook and he is teaching her to be an excellent cook, but I don't belong in the kitchen," she says.

"We're really like a three-adult household."

Describing her relationship with Jemma, she says: "I just always say picture your best friend, only you have a romantic relationship as well."

Ms Block came to polyamory exactly the way people say not to do it - after cheating on her husband.

After finishing university and marrying, she says that what she calls the "Cinderella path" of monogamy did not feel right to her. She knew she was bisexual, and three years into her marriage, she says, she started a relationship with a woman.

When Christopher found out he was angry, not because she had had a sexual relationship with someone else, but because she had been dishonest with him, she says.

'Is this weird?'

After working it out with him, the couple shared a girlfriend for a time, then she dated other people, Ms Block says.

"From the very beginning, he and I found ourselves saying, 'is this weird that it isn't weird?'" she says. "We were worried the other shoe would drop."

But it didn't. Ms Block has been with Jemma for five and a half years. She and Christopher will be married for 15 years this year.

Ms Block struggles to explain how she can be satisfied with her husband, yet still want another person in her life - and her bed.

"All I know is that I continue to love him and want to be married to him and want to be with him, but I also have this desire to have another partner," she says.

"This is so much less about sex than people who aren't in these relationships know."