For any couple, working together as well as living together can put a strain on a relationship. But if you're in the public eye as well, it can prove too much. Perhaps, as Steve Pratt advises, its best to stay together - don't play together.

Ben and J-Lo are together again. Don't bother digging out that box of confetti, the showbiz couple are only getting up close and personal on screen, as their film Gigli is released in British cinemas.

That's where their troubles began. Movie couples - married or not - who play together in front of the cameras have a hard time staying together away from work.

The prospect of the on-off wedding of glamorous twosome Ben Affleck and Jennifer Lopez has been entertaining us for weeks as the will they or won't they? suspense mounted as the big day came and went, with the couple thousands of miles apart when they should have been tying the knot.

Perhaps no one should be surprised it never happened. Not just because of J-Lo's poor marriage record or Affleck's seeming inability to look the other way when a beautiful girl passes by. They should have taken note that the odds of a movie star marriage lasting, when both want to stay on top in Hollywood, are not good.

There are exceptions, like Paul Newman and Joanne Woodward, who wed in 1958 and are still a Mr and Mrs despite working together. More often than not, star couples separate in as big a blaze of publicity as when they wed.

Consider Meg Ryan, whose marriage to Dennis Quaid ended following her affair with Proof Of Life co-star Russell Crowe. Worse still, as far as backers were concerned, was that the hoo-ha failed to persuade audiences to see the movie, proving that not all publicity is good publicity.

Tom Cruise and Nicole Kidman had marriage made in movie heaven, joining the world's biggest box-office draw and a rising, glamorous Australian actress. They met on the motor racing movie Days Of Thunder, and starred together again in the epic Far And Away. They fell in love, they married, they adopted two children, they were the perfect family.

Then came Eyes Wide Shut, Stanley Kubrick's erotic drama about sexual jealousy with Cruise and Kidman playing a married couple. They lived and breathed the movie day in and day out, playing out this intense and explicit sexual story in front of the cameras for nearly two years.

Soon after the movie was released, the pair split up. The pressure of constantly being together, play-acting a marriage going through a crisis, was seen as a contribution to the break-up. Making Eyes Wide Shut put an intolerable strain on their relationship.

Kidman's career has taken off since the divorce, and she won an Oscar as Virginia Woolf in The Hours. The suspicion is that being married to the biggest movie star in the world held back her career. She was talked about as Mrs Cruise which, perhaps subconsciously, caused resentment. Then their public split certainly served to expose her to a wider audience than her screen roles until then.

Affleck and J-Lo didn't even make it up the aisle. Poor reaction to their starring vehicle Gigli can't have helped. The $54m comedy took a paltry $3.8m in its opening US weekend, a clear signal that audiences weren't interested in seeing them together. A legal union might have been bad for both of their careers.

Married movie stars fall out in public, but their problems are universal, according to Relate, the marriage guidance organisation. The dilemmas of couples working together is a subject that arises frequently in counselling sessions.

"It's about the boundaries and the personal relationship you have at work. Boundaries can become quite blurred, with people treating each other as co-workers or employees in the home," says Relate counsellor Denise.

"Arguments at home can spill over into the workplace. The other thing is recognising what belongs in the workplace and what belongs in the home."

Rivalry at work has to be addressed as well. Individual strengths and weaknesses that come into play at work, don't necessarily have a place at home.

Finding the right balance takes time, she says. "The best thing, if you are working together, is to have some couple time that's completely separate. Don't just socialise with work people, and realise that both of you are going to have different expertise in different areas.

"If you are both in something like advertising, which is highly creative and competitive, you can be tempted to be secretive about your ideas."

Leaving work behind, she adds, is obviously more difficult for actors. "They can be supportive, but actors, on the whole, have to be up there on the stage and need to be out there entertaining their public, or they feel a big failure. And if one becomes more successful than the other that can compound that feeling and can cause conflict between the two."

It almost sounds as if movie star marriages are doomed from the words "I do". Many a split has had its roots on a film set, when one or both of the people involved are wed to others. Richard Burton and Elizabeth Taylor became one of the most famous double acts on and off the screen following the Cleopatra scandal.

Taylor was starring in the epic Cleopatra, having recovered from a near-fatal illness that delayed filming and caused Burton to replace the actor originally cast as Mark Antony. During shooting in Rome, the most expensive film ever made became the most notorious when rumours emerged that Taylor, married to singer Eddie Fisher at the time, was romantically involved with her Welsh co-star.

They married - and divorced several times - and made a string of pictures together, although their fiery relationship was often more exciting than their movies. Their partnership gave Burton, until then a classical stage actor, Hollywood stardom and Taylor a role in a screen team that was artistically (and financially) rewarding. But, of course, it didn't last.

Screen Lara Croft, Angelina Jolie, is shaping up as the new Taylor. She even quipped: "I'm not very good at marriage" during promotional duties for her second Tomb Raider adventure this summer.

At 20, she married Trainspotting star Jonny Lee Miller after they met on the set of computer drama Hackers. Five years later, she wed Pushing Tin co-star Billy Bob Thornton. He was 20 years older, already four-times married and engaged to another actress at the time. None of that stopped wedding bells ringing out for him and Angelina.

They missed no opportunity to tell everyone they were madly in love. She wore a vial of his blood around her neck. Two years later, they were madly out of love. Now single again, Jolie has eyes only for her adopted Cambodian son Maddox.

If your partner is also your director, the problems are multiplied. Madonna and actor husband Sean Penn split after Shanghai Surprise, generally regarded as one of the worst movies ever. To most, it was no surprise as the singer's attempts to forge a film career have been mostly embarrassing.

The bonus of marrying Brit Guy Ritchie was that he was the hot, hip director of Lock, Stock And Two Smoking Barrels. Alas, his attempt to give Mrs Ritchie credibility as an actress failed. He directed her in Swept Away, only to have the movie laughed off screen in the US and released straight to video in this country.

Where other marriages might have suffered, theirs has survived the humiliation of a film flop - though the idea of Ritchie risking his reputation by directing his wife again seems as likely as Affleck and J-Lo getting hitched.