Mike Green remembers back in 2005 when his then-wife asked him to add text messages to their cell phone plan. Green, of Mankato, Minn., had no interest, but his wife went ahead and signed up. After that, he says, she seemed to text all the time -- when he'd come home from his evening shift for dinner, when they were cruising the shopping mall.
"Actually, one of my buddies asked me if it was a big deal she was texting all these people," he says. "I said 'No, I trust her, so why would I even worry?'"
Then Green saw a phone bill. He says there were hundreds of texts, a long list of numbers that meant nothing to him. Over time, there was one number more than any other. It was a colleague his wife had started an affair with and for whom she eventually left him.
"Because I was gone at nights, she used him as her support system," he says. "She would talk to him about things."
It turns out that text messages and social media sites like Facebook and MySpace -- so beloved for bringing people together -- can also drive a wedge between couples.
"We hear this so commonly in our offices that it began to feel like there was a CD player hitting repeat," says Tara Fritsch, a marriage therapist in Edmond, Okla.
To be sure, she says, texting doesn't break up a marriage, people do. But opportunity is a key predictor of infidelity, and social media have increased opportunity exponentially. Does something remind you of an old flame? You can reconnect in the few seconds it takes to type the person's name into Facebook.
"Twenty years ago," Fritsch says, "if you really thought a co-worker was interesting, and later on that evening you thought of them and wanted to say, 'Hey, how you doing?' Then you would have to ask yourself, 'Is it really appropriate to call them at home? What if their spouse answers? What am I thinking about?' "
Today, those stopgaps are gone. Texts and e-mails can be delivered privately. Sending a little message, at least at first, can feel so innocent.
In fact, as Lindsay James of Fort Worth, Texas, learned the hard way that a partner can easily carry on an affair in the same house, even the same room.
"That's what would upset me more than anything," James says. "It's like, 'Wow, he was sitting right next to me, we were watching a movie, and [he was] talking to someone else -- and I had no idea.' "
The irony, James says, is that her boyfriend admitted he would never have had the nerve to approach other women in person.
Green says he was stunned at how quickly his wife's texting relationship turned into an affair. That's typical. Bob Rosenwein of Lehigh University has found that people communicating online often fall for each other in about a week. That's two or three times as fast -- on average -- as those courting face-to-face.
"When you don't have nonverbal communication, the likelihood of being able to disclose at a deeper level is greater, because there's less inhibition," Rosenwein says. "So it's going to feel like a more intimate relationship."
Therapist Fritsch says this makes it easier for some with no intention of starting an affair to unwittingly cross a line. Often this leads to a physical affair but even without that, some marriages are damaged.
"The emotional loss -- the lies that have hidden the emotional connection -- is just as painful as if their spouse had actually gone out and met with someone," Fritsch says.
After his divorce, Green got his own social media accounts and also started texting. He soon learned how easy and addictive it is.
"It's a rush," Green says. "It's a good feeling to have this constant attention poured upon you by anyone that you get to text all the time. And I find myself still loving to get texts from females, and I text, text, text, back and forth."
Yet Green says he's wary about another intimate relationship. He wants to trust again. Every time a girlfriend texts someone else, he can't help but feel suspicious.