In the minds of many, the definition of marital infidelity is pretty straightforward: If you have a sexual relationship with someone other than your spouse, you've cheated.
But marriage counselors are adding more gray to that definition by identifying nonphysical ways of being unfaithful - such as forming attachments that rob a spouse of emotional intimacy.
These aren't the bonds forged on a "girls' night out," but rather those formed between two co-workers who, for example, share everything - their aspirations, their marriage woes - and keep the extent of their friendship a secret from their spouses.
"If you are skimming off the aspects of your inner life ... and reserving them for your 'friend,' you are cheating your spouse of intimacy," says William Doherty, a professor of family social science at the University of Minnesota.
Some experts have gone as far as to call this a new crisis of infidelity - one that is changing the way gender relationships are viewed. That's the position taken by the late Shirley Glass, a researcher and family therapist whose last book was published earlier this year, before her death.
Dr. Glass found it wasn't just thrill seekers or those unhappy in marriage who are prone to emotional cheating.
"The new infidelity is between people who unwittingly form deep, passionate connections before realizing that they've crossed the line from platonic friendship into romantic love," she wrote in "NOT 'Just Friends': Protect Your Relationship From Infidelity and Heal the Trauma of Betrayal."
Today, there are greater opportunities for intimate relationships to form between men and women, and for the boundaries between platonic and romantic feelings to blur, she and others argue. Changes in the workforce have brought more women into offices at all levels, and the Internet has made it far easier to quickly form bonds with strangers.
In both cases, it can be easy to meet someone and suspend reality. On the Internet a contact can become a romanticized ideal without faults. And in the office, an intriguing co-worker can seem more exciting than a spouse with whom you have to pay bills and fix plumbing.
"An emotional affair to me can be as damaging as a sexual affair, because an emotional connection is what people really want," says Rona Subotnik, a marriage and family therapist in Palm Desert, Calif., and author of books on infidelity, including Internet relationships.
The workplace is a particularly fertile ground for cheating, experts say. By some accounts, the office is replacing the local pub as the place where men and women meet - and cheat. About 8 million to 10 million new relationships are formed annually in offices, according to Dennis Powers, a professor of business law at Southern Oregon University in Ashland, and author of the 1998 book "The Office Romance."
That figure is for singles entering relationships, but the same environment might easily influence those who are married. Working closely together on a project, for example, can be enticing, as can simply being around someone everyday who shares similar goals and aspirations.
An "emotional affair" tends to involve sexual attraction - even if not acted on - and secrecy on the part of a married participant, therapists note. It can be difficult in the workplace to realize an emotional affair is developing, says Professor Doherty, because there's usually not a big event, like a sexual encounter, to signal that you've turned the corner.
Even so, not everyone believes that interaction between men and women in the workplace spells disaster. "The mere fact that a person has friendships from work by itself can't be considered unethical. The question is where it crosses the line," says Professor Powers.
Some observers note that the issue of emotional affairs is prompting new rules for gender relationships - but not everyone thinks more rules are the best idea. Laura Kipnis, author of the recent book, "Against Love: A Polemic," questions whether it is right for one partner to control another's autonomy or intimacies too much. "To what extent is it ethical ... that their movements or associations should be restricted to appease my own anxiety or insecurity?" she asks.
For her part, Glass offers a framework for separating home and work relationships, noting that fidelity is about maintaining appropriate boundaries. Among her suggestions: discuss relationship issues at home, don't lunch or take private coffee breaks with the same person all the time, discuss your online friendships with your partner, and surround yourself with friends who are happily married and who are committed to the idea of fidelity.
Has your friendship become an emotional affair?
1. Do you confide more to your friend than to your partner about how your day went?
2. Do you discuss negative feelings or intimate details about your marriage with your friend but not with your partner?
3. Are you open with your partner about the extent of your involvement with your friend?
4. Would you feel comfortable if your partner heard your conversation with your friend?
5. Would you feel comfortable if your partner saw a videotape of your meetings?
6. Are you aware of sexual tensions in this friendship?
7. Do you and your friend touch differently when you're alone than in front of others?
8. Are you in love with your friend?
Source: "NOT 'Just Friends,' " by Shirley Glass