The key to a happy and successful marriage is allowing your partner to have sex with other people.
That's according to a team of psychologists, who believe adultery can put the spark back into a long-term relationship.
Elie Finkel, of the Department of Pyschology at Northwestern University in Illinois in the US, also advised bored couples to live apart for a period to rekindle their romance.
And he said partners who are no longer sexually attracted to each other should also consider a "non-monogamous" relationship.
He said: "It may be that your spouse is a terrific source of social support and intellectual stimulation, but you haven't had sex for the last five years and neither of you thinks that's adequate.
"So you could say, that's one of the needs I am going to fulfil elsewhere. I don't recommend cheating, but an openly consensual, non-monagamous relationship, that may very well be functional."
In his paper, 'Suffocation of Marriage', Prof Finkel argued that modern-day married couples are feeling less fulfilled because they expect too much from their partners.
He told the annual conference of the American Association of the Advancement of Science that couples are not only looking for a friend, but someone who inspires them creatively and can help them achieve their long-term career and personal goals.
The research comes after therapists at Relationships Ireland said they are anticipating a surge in demand for their services following fall-outs from the discovery of extra-marital affairs over Valentine's Day.
Meanwhile, another American study has found that a blazing row can help those caught up in an unhappy relationship.Professor Keith Sanford, of Baylor University in the US, quizzed 734 couples for the research, which was published in the Journal of Social and Personal Relationships.
He said: "People in satisfying relationships resolved conflicts regardless of whether they used negative communication or not.
"In contrast, people in unhappy relationships tended to have big conflicts, and they tended to have trouble resolving their conflicts."