We used to know what infidelity was: sex with someone other than your mate.
But the 21st century seems to have blurred those clear-cut lines. Is having lunch every day with an opposite-sex work friend a breach of marital trust? What about a flirtation online? If there's no sex, is it really cheating?
Such questions arise as societal and psychological pressures challenge deep-rooted ideas about the nature of infidelity. "We are as a society finally coming to grips with what it means to be faithful," says Douglas Snyder, a psychologist at Texas A&M University-College Station. "It doesn't just mean to have sex with someone else."
Many psychologists and family experts say that infidelity today is not just about sex but about trust, betrayal and marital disloyalty, even if adultery is not part of the picture. They add that marriages are more vulnerable than they were decades ago: In tough economic times, couples work harder to make ends meet, which often leaves little time or energy to nurture the relationship. Movies and TV seem to glamorize affairs and make marriage appear dull. And the Internet offers a new frontier, with the pseudo-intimacy of cyber-relationships, as well as greater access to pornography.
Added to all this: Research suggests those who have affairs aren't necessarily unhappy with their partners.
"People are getting this incredible message that if you're not hot and having a certain kind of Hollywood-style sex, something is wrong with you," says clinical psychologist Sue Johnson of Ottawa, Canada.
Johnson, author of the book Hold Me Tight, and psychiatrist Frank Pittman are among presenters at the Smart Marriages conference, which begins Wednesday in San Francisco and will include sessions on extramarital affairs.
"I run across people who think everybody is messing around and something is wrong if they're not doing it, too," says Pittman, of Atlanta. "People get the idea from the media that it's a normal thing and anyone not doing it is missing out on life's goodies."
A study last fall by the online research firm Insight Express found that 89% of 1,000 adults ages 25 to 65 believe monogamy is a realistic goal. But 75% say the lifestyles of young Hollywood stars set a bad example, and just 26% believe television portrays committed relationships in a positive light.
Pop culture expert Gary Hoppenstand, an American studies professor at Michigan State University in East Lansing, has analyzed romantic comedies of the 1950s and '60s and found "the disintegration of the traditional American household and adultery as a common theme."
He cites movies such as 1955's The Seven Year Itch; 1967's A Guide for the Married Man, Divorce American Style and The Graduate; and 1969's Bob & Carol & Ted & Alice as examples of the assault on marriage.
How common are affairs?
It's difficult to gauge whether affairs are indeed more common or just more openly discussed, especially in light of news stories about celebrities and public figures that make it appear cheating is on the rise. Research on infidelity is largely based on surveys in which people self-report, so they may or may not tell the truth and people may not all agree on definitions, such as whether to count a one-night stand as an affair or whether oral sex is really sex.
The most recent large-scale data are from the 1998 General Social Survey, conducted by the National Opinion Research Center at the University of Chicago. It found that of 2,169 people who had been married at some point, 17.9% reported sexual infidelity.
Some researchers say there's a 50-50 chance today that one partner will have an affair during a marriage; that includes non-physical relationships.
But Snyder adds that there is a risk in overestimating the prevalence or acceptability of affairs.
"It becomes a self-fulfilling prophecy the more we imply these are commonplace and everybody is doing it," he says.
"The big thing that made marriages vulnerable in the past was that we expected so little, and today the big problem is we expect so much," says Stephanie Coontz, director of research at the non-profit Council on Contemporary Families, a group for researchers and clinicians.
Those expectations focus on the spouse as best friend or soul mate, which adds to the pressure on spouses and makes marriages more vulnerable, experts say.
"We expect one person to give us what an entire community used to -- family life and stability and economic support and be a trusted confidant and passionate lover and experience adventure with the same person," says Esther Perel, a couples and family therapist in New York City.
Marriage takes energy
Thomas Bradbury of the Relationship Institute at the University of California-Los Angeles says today's economy further intensifies the problem.
"Now we have two people who are struggling mightily under often difficult circumstances to keep their marriages afloat," he says. "Even if the internal dynamics of the marriage haven't changed that much, if suddenly people are less able to generate the energy that it takes, those relationships are going to struggle."
Relationships that involve emotional sharing, whether in person or online, but that exclude your spouse can be dangerous territory, says Pittman, who has been married 48 years. He says getting close to someone else to fill an unmet need for intimacy "pulls you out of your marriage further and further."
Such outside emotional connections have been called "emotional affairs"-- and growing numbers of married people are in such relationships, says Ronald Potter-Efron, a clinical psychotherapist in Eau Claire, Wis. He and his wife have co-authored a book about the phenomenon, called The Emotional Affair, to be published in January.
Many people involved in such relationships say their spouses are irrationally jealous, Potter-Efron says, but the spouse says "it just doesn't feel right."
Natalie James-Tapley, 37, of Miami knows the feeling. She says she and her former husband have been divorced four years, after a series of separations. She believes he was emotionally involved with a co-worker.
"If they're now turning to someone else for that emotional support, then it is a form of cheating," she says.
Retired firefighter Pete Wright, 53, of Greenville, S.C., believes "deceiving your spouse in any way is asking for problems, even if no sex is involved."
Wright, who's been married 25 years, has seen what happens if the virtual becomes real: A friend's wife had an online relationship that led to divorce, he says.
"I'm sure it started out as friendly conversation, but eventually it evolved into something that doomed their marriage."
Cyber-affairs may appear safe and manageable, but people may get more involved than they planned, researchers say.
"They are reaching out for contact or connection of some kind. They're not necessarily looking for sexual connection," says Peggy Vaughan of San Diego, author of Preventing Affairs.
"The big debate today is how real is the virtual."
Ed Diener, a psychology professor at the University of Illinois-Urbana-Champaign and a leader in the field of happiness research, says people are more in search of thrills today and may think they're unhappy when things are just OK.
Happiness is misunderstood
"People misunderstand happiness now more and more," says Diener, co-author of Happiness: Unlocking the Mysteries of Psychological Wealth, out in September.
"We used to think happiness was a kind of contentment and life satisfaction. Now we've come to define it as a really high-arousal kind of excitement. 'How are you?' 'Great! Super!' -- these words are very extreme, but they're the normal answer now."
The need for extreme stimulation may be one reason online pornography is becoming more an issue in marriage, some say.
Bill Maier, a clinical psychologist at Focus on the Family, a Colorado Springs organization devoted to Christian family values, says calls about pornography to the group's counseling center have doubled in the past five years as the Internet has made sexually explicit images more easily accessible.
Two 1988 studies about the effect of prolonged consumption of pornography found that for both men and women, porn fueled unrealistic expectations about what sex should be and what their partners should be like, and made them less satisfied overall. Those studies appeared in the Journal of Family Issues and the Journal of Applied Social Psychology well before the Internet was widely used.
Michael Leahy of Herndon, Va., says his work in the early days of the tech industry made it easy to access pornography. Leahy details how he became addicted to porn, which he says led to his divorce, in the book Porn Nation.
When he felt tension or stress, "pornography was always there as a mood-altering drug. And it was something I never shared with my wife. She had no idea I was doing that," says Leahy, 50.
Although some experts claim they can "affair-proof" marriages, Snyder, co-author of the 2007 book Getting Past the Affair, says one fact cannot be ignored:
"Marriage, on the excitement dimension, cannot compete with an affair. Couples need to come to grips with the reality that the passion and excitement of romance and courtship and the honeymoon is not going to last."
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