My husband and I haven't been getting along so well lately....

This is the public face of marital discord. It's the kind of secret we entrust to friends with a rueful smile, a roll of the eyes, perhaps a hint of resignation. He's driving me crazy, but what can you do? It's perfectly acceptable—funny, even. After all, haven't we all been there?

And then there's the kind of marital secret we don't dare tell our friends because it's too potent, too painful, too threatening. It involves a betrayal of the most intimate of human relationships, of the trust that is the very bedrock of most coupled people's lives. He's busy watching porn while he's supposed to be watching the baby. Or, he's so boring in bed I have to fake it with him. Or, I've attached a GPS to the underside of his car to see where he's going. Or, I never thought I'd be the one having an affair.

These days, more and more Americans seem to have the latter kind of secret, at least if you believe last year's headline-making study that cheating is on the rise in some age groups. The research was based on data from 1991 to 2006 from the General Social Survey (the National Science Foundation's biennial snapshot of the behaviors and opinions of American adults): Although lifetime infidelity rates hover around 25 percent for men and 15 percent for women, rates for women under 35 are on the rise, and men over 69 are straying more than ever before. The number of unfaithful wives under 30 increased by 20 percent; husbands, by 45 percent.

We can probably thank Viagra for the surge in extracurricular activity among older men; as for the younger women, experts point to a loosening of cultural mores and to women's increasing economic independence—the assumption being that an economically dependent woman is more likely to think she can't afford the risk.

And then there's access. Digital technology is the most interesting thing that's happened to infidelity since key parties. By now we all know that thanks to e-mail, texting, cell phones, and the Internet, stepping out on your significant other has never been easier. You can find websites like AshleyMadison.com, which caters to married people who want to have affairs, and Casual Encounters on Craigslist, which caters to anyone who wants to do practically anything. We know, too, that it's never been more perilous, because every technological innovation that enables the cheater also makes it that much easier to be caught. But what gets lost in the juicy drama of high-tech hookups and cybersleuthing is how technology makes it possible for people dealing with infidelity simply to talk to one another.

Google the words "infidelity" and "discussion group," and you'll come up with more than 10,000 hits, including dozens of websites where people share their deepest, most painful marital secrets. SurvivingInfidelity.com, MarriageBilders.com, WomanSavers.com—the list goes on. And the permutations are endless. On iVillage, the boards grouped under the rubric "relationship problems" include Married Without Romance, Betrayed Spouses Support, Betrayed Girlfriends Support, Cyber-Cheating & Emotional Affairs, Should I Stay or Should I Go, Life After Betrayal, Surviving Divorce & Separation, My Affair Support, and After the Affair. Infidelity chat rooms have become the agnostic equivalent of the old-school Catholic confessional. When the deepest trust in your life has been broken, you look for safety among perfect strangers.

The phenomenon of infidelity forums sits squarely at the intersection of morality, technology, and secrecy. Now that alcoholism and drug addiction are socially acceptable sins, infidelity is one of the few cultural taboos left. According to David Popenoe, founder and co-director of the National Marriage Project at Rutgers University, while infidelity is far more prevalent today, attitudes about it haven't budged since the '50s. "Ninety percent of people think fidelity is absolutely the basic part of marriage," says Popenoe. "It's almost a litmus test for success." Once cheating enters the picture, people can become as secretive with friends and family as an adulterer is with his or her mate, but Popenoe doesn't consider Web posts replacements for human dialogue. Rather, in an era of smaller families and looser friendships, the Web, he says, is a pipeline to a "huge group of people who have similar experiences."

On UrbanBaby.com (a site that began as a place to discuss your kids but rapidly became a place to discuss anything family- and marriage-related), one woman contemplating an affair posted a cry for help. Another woman in a similar situation replied, "I never discuss this IRL [in real life]. Too personal. It's a shame, though, because so many of us go through things like this."

"Infidelity triggers everyone's morality," says psychotherapist Jane Greer, PhD, author of How Could You Do This to Me? Learning to Trust After Betrayal. "Loved ones are invested in your marriage; they can't give you nonjudgmental support. Yet being a victim or perpetrator of adultery is one of the times in a person's life when she most needs to talk—without the risk of anger, criticism, or blame. And that perpetuates the need to conceal."

So we type. And type. And type some more.

In the language of online message boards devoted to infidelity, BS is the betrayed spouse. EMA stands for extramarital affair. There are PAs and EAs—physical affairs and emotional affairs, either of which may be precipitated by an MLC: midlife crisis. D-Day is discovery day—the day you find out about an affair. OM is the other man; OW, the other woman; OMW, the other man's wife. AP is affair partner. WH is wandering husband. The WS (wayward spouse) is said to be in the "affair fog"—so consumed and distracted by the affair that he or she becomes irrational. They can't even trust themselves.

The forums, which are dominated by women (with the occasional DH, or dear husband, weighing in), are part support group, part reality check. As in any social community, friendships are made, advice offered and taken, even though the "posters" know each other only by their chat-room handles. Veteran posters are armchair psychologists who have co-opted the language of addiction: Adulterers trying to repair their marriages are "in recovery" and worry about "triggers" that may resurrect their spouse's rage.

Each site has its own attitude. WomanSavers.com has feature pages devoted to outing the betrayers. Users can post a picture of a cheating man (a sort of America's most wanted for two-timers), and the most popular message board is called Catch a Cheater. The claws come out. In one thread, scorned wives name the other woman who they claimed cheated with or stole their husbands, complete with their cities, states, and physical descriptions, none of them flattering. When one wife dubbed the OW a "manhole my ex-husband kept falling into," posters gleefully adopted the term.

At the other end of the civility spectrum, SurvivingInfidelity.com calls itself "your safe place to come and share your pain and feeling of isolation upon discovery of betrayal." Wayward spouses are welcome to post, "provided they are remorseful and committed to healing." Its forums have less venom, but the pain of betrayal, and its effect on an entire family, comes through loud and clear. One distraught wife stated her anguish with a candid eloquence:

"I am really having trouble moving past this. Specifically, not being down and crying about this anymore. D-day was two weeks ago, and now we are back into the regular routine of him going to work, kids going to school, and my life as a stay-at-home mom."

"However, I keep getting hit with the stomach punch of despair at odd times. So I still cry, or just need to get in my bed for a little while. I feel really bad that my kids are seeing me this way. They don't know why I'm sad, think I'm sick, and try to comfort me. I am trying to hold it together for them."

"Each night after the kids go to bed, my WH and I have time together to just sit and watch TV. And of course, that's when my questions start. And his lack of answers. Every night."

Usually sincerity is met with well-meaning advice: On UrbanBaby.com, the question "When do you know it's time to separate/divorce?" got 45 quick replies, ranging from "Have you tried counseling?" to "Do you give oral? ... It really helps smooth out the rough edges." But there are always a few Judgy Judgertons whose idea of nuance is "Kick him to the curb!"

Whatever the case, the question of trust is front and center. Consider this thread on MarriageBuilders.com. The OP (original poster) writes that she busted her husband sending sexual e-mails to women he met online, using a secret account. Another woman becomes her been-there, felt-that sounding board. The dialogue has the intimacy of two lifelong friends, not anonymous strangers who just met.

OP: I want to be angry, but to be honest, my heart is just broken.

Reply: Well, don't let it be broken just yet. You need more info. How is the rest of the marriage?

OP: Great. I never suspected it and was in total shock when I saw it. It's completely out of his character. We tried to talk it out. He has no reason, no excuse. It wasn't like he would ever actually see those girls—he says. He says he's genuinely sorry, and I have the sneaking suspicion he wants it left at that. How can I get answers from him? I know there has to be some even if they aren't the ones I want them to be.

Reply: Of course he wants it left like that—to just forget it ever happened. But don't let this be swept under the rug.

OP: I have blocked all sites like the one that got him in trouble. I hate to feel as though I'm just controlling his urge. Shouldn't it not be there at all?

Reply: I wouldn't block the sites; I would watch what he does. You want to find out if he would like to lead a secret life, and you can't just ask him, because they lie.

The psychologist Erik Erikson, who advanced our understanding of human psychosocial development, theorized that because we are born helpless, our first object of trust is our mothers—and that if they live up to our trust, meeting our earliest needs (for food, shelter, affection, attention), we can grow up to have faith in others. (Ironically, Erikson's mother became pregnant with him during an extramarital affair.)

Trust is essential to human experience. A million years ago, while cavemen were out hunting mastodons, their female counterparts were slaving away back in the cave, perpetuating the species and creating clans. Clans became increasingly generous and trusting, leading to the creation of entire cultures.

Paul J. Zak, a professor at Claremont Graduate University in Riverside, California, who specializes in the neuroscience of trust, argues that women spearheaded this evolution. The reason: oxytocin, the hormone that promotes generosity and sociability. Childbirth, breastfeeding, and ovulation cause oxytocin to surge. Men, on the other hand, tend to be heavy on testosterone, which actually blocks the release of oxytocin. In one experiment, Zak found that when researchers boosted oxytocin levels in men's brains via a nasal spray, they became far more empathetic, generous, and eager to entrust strangers with their money. "Oxytocin makes us care for people around us," says Zak, adding that the positive emotions triggered by this feeling of goodwill release even more oxytocin, which he calls the trust hormone.

As Zak sees it, there's a reason that most of the people who frequent infidelity forums are women. For one thing, since oxytocin promotes monogamy, they constitute a majority of the betrayed parties. "People who feel betrayed are very isolated and vulnerable. Women in particular want to reach out to some kind of group. They tend to like to get together and talk it through. They form random groups quite easily. So who do they turn to? Almost anybody."

Among strangers, cheaters and cheatees can find comfort, support, and affirmation. But the woman who confesses her own transgressions can't trust that she'll get a sympathetic hearing. On iVillage a few years back, a flame war broke out when a contingent of women from the Betrayed Spouse Support board began lurking on the My Affair board for clues to their situation—and suspected, based on what they read there, that certain My Affair posters were the actual women cheating with their husbands. This despite the fact that everyone involved was anonymous and that the plot lines of affairs tend— let's face it—to repeat themselves.

But the forums are generally self-regulating, leaving the original poster to pick and choose from a range of reactions. On UrbanBaby.com, one married woman's shame-filled confession of kissing another man generated a score of condemnations ("Your soul will be crushed"), a smattering of "Don't judge yourself so harshly," and, finally, "This is what this site is perfect for, what anonymity is good for. OP has exactly the right take on this—she knows she screwed up, she's not going to complicate her life or hurt anyone by telling anyone IRL. So here she gets to 'talk' about it and make smart choices for herself and her family. Bravo!"

On some sites, there is no way to know who is posting; there are no identifying names, and participants keep their identifying information to a minimum. "There are times when you just want to get a fresh perspective—or ask the crowd," says Justine Reese, senior product manager at UrbanBaby.com. "You can throw up a question and have 10 responses in 10 minutes." The idea of advice-taking on message boards is "pick what you like and avoid the rest." Even if you don't trust another poster's advice, you usually trust that she's being honest.

On other sites—generally those on which posters have handles—connecting is the point. Women get to know one another, or at least their points of view, and form true bonds, exchanging phone numbers and personal e-mail addresses. I posted a message on iVillage's Betrayed Spouses' Support forum in which I asked about friendships formed. "We are all cybersisters," one user wrote back. "So many of these women have become my good friends," wrote another. "Friends who are there, friends who can identify with the many emotions I go through. Friends who do not judge. Friends who I can lay it all out there to. I would not be here if it were not for this site."

In short, she feels she can trust them.

We are, all of us, the most contradictory of creatures. We need each other, we need to talk, to connect. But when our most intimate and profound bond of trust has been broken, we also need absolute safety to talk about our deepest hopes, fears—and shames. So how do you know if you can trust your invisible audience? Maybe it doesn't matter. Maybe what matters the most is that you dared to speak up and that someone out there was listening.

From the March 2009 issue of O, The Oprah Magazine.