Is your spouse texting -- or cheating?

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Alison's husband knew she was having an affair. After all, she'd confessed the whole thing.

But her marriage only fell apart after he opened her laptop and found the many, many passionate e-mails she'd exchanged with her co-worker.

"That was more crushing than anything," Alison said. Now in her 40s, she's a media professional living in a well-heeled Boston suburb, and her name has been changed for this article. "It's one thing to know the person is having a relationship — it's another thing to actually see the communication, because then they realize you're saying things to your lover you'd never say to them."

The real-life extramarital sex she'd had, in other words, was less damning than the online flirting she'd committed to text.

This is the state of infidelity, 20 years into the digital age. Post-Anthony Weiner, post-Ashley Madison, our "real lives" are lived as much online as off — and the difference between the two grows ever more blurred. When your phone is always in your hand, are you ever really offline? Is it harder to be faithful to your significant other when the two of you are never really alone?

Just ask Dana Prestone, of Rockwell Investigations in Wakefield. He's been investigating errant husbands and wives since 1998 — the days of AOL, dial-up, and beepers. In that time, his business has changed.

"It's harder to stay away from technology now," he said. Constant communication creates constant suspicion: "If your husband or wife calls and you're not there to pick up, years ago it just meant you just weren't available. Now, you must be up to something."

Cheating and technology have engaged in a low-key arms race: When landlines got caller ID, beepers became the communication method of choice. Now that no one uses a beeper, trysting couples exchange burner phones or use passwords to hide texts and e-mails from snooping spouses. With modern tech, "It's easier to get caught if you're not smart," Prestone said, "but if you are smart, it's also easier to hide what you're doing."

Technology also brings temptation: while Tindr offers up a smorgasbord of friendly strangers, Facebook puts us within messaging distance of every old flame. Many of Prestone's targets find themselves ensnared by high school crushes: "Naturally, you're curious what they look like now. Then you're meeting them for coffee. Three weeks later you're in a motel room together."

Where trysting couples used to have to work out arcane signals for communication — letting the house phone ring once and then hanging up, for example — now there are a plethora of apps offering discreet communication.

"You can be cheating with someone while you're sitting right next to your partner," said Katherine M. Hertlein, a therapist and researcher at University of Nevada. She's been studying the intersection of technology and relationships for years. Once, she said, she noticed a client fiddling with a phone during couples' therapy — he was texting his lover while his wife was talking about their relationship problems.

Like Prestone, Hertlein says that the constant availability of the Internet is an issue. In the early days of personal computers, marriage counselors might tell a couple to keep the computer in the living room to reduce the temptation to message a forbidden liaison.

"Now, it's no longer about 'removing the computer removes the threat,'" she said. "We have it on phones, on watches — everywhere."

Hertlein became interested in digital infidelity in the early 2000s, when the online massive multiplayer game World of Warcraft was at its height (a film based on the game's fantasy setting opens in June). Her husband, a techie, was an avid player.

Together, he and friends he'd never met in person would lead raids on computer-generated opponents, a task which brought them solidarity but left Hertlein out in the cold. "I was a Warcraft widow," she said.

She began to realize that the comraderie of the game wasn't a fantasy at all — it was very real. Going through shared experience, even a virtual one, was creating new and intense relationships for her husband. Warcraft, in short, was a force that gave him meaning.

Part of the problem, she added, is the ambiguity of online contact.

"Couples have no idea whether or not they've been cheated on," she said. If a relationship predates the Internet, the simple rules it started out with — no kissing other people, no sex with other people — might need to be renegotiated to include no sexting other people or no sending nude pics.

"Technology changes all the time," Hertlein said. "So if you're planning to be in a long-term relationship and you've got a definition of what it means to be unfaithful, in 10 years when technology is vastly different, you're going to have to have that conversation again."

Where Prestone sees a change in how accessible online communication is, Hertlein sees a change in the quality of that communication. Online, she said, people become intimate more quickly and in ways they wouldn't consider otherwise.

"There is a process by which people disclose more," she said. "They disclose more and more quickly and with greater depth, because there isn't a physical presence — you're not looking at someone and talking to them and thinking about their hair. So then there is an opportunity for people to develop relationships much more quickly. The next thing you know, they feel so connected to someone, and they can't understand how they got there so quickly."

Lying, too, becomes easier in text-based communication, without facial expressions and behavioral tells to put words into context. So does fantasy. You can text a lover that you're alone, in the bath with a glass of wine, even as you're standing in line at the grocery store.

That kind of freedom "creates this magical relationship," Hertlein said. "And that's the thing about infidelity — in general, it's about the fantasy of the person. It's harder for the spouse to match the fantasy."

In her practice, Hertlein says, she uses the very tech that can break a couple up to heal the rift after an infidelity. She forces them exchange e-mails throughout the day, in which they role-play an imaginary date. She swears it works: It builds intimacy just the way online affairs do, through text and collaborative fantasy. Plus, she said, "when their partner is attending to them, they know they're not texting someone else."

As for Alison, she eventually found herself on the other side of the equation when she started to think her husband — not the same husband she'd cheated on, but the one after him — was cruising an online dating service. Hoping to catch him, she created a profile.

"I was going to bait him," she said. "So in the profile where you fill out facts about yourself, I only put down cuts of meats." She figured that was bizarre enough that it would only appeal to her husband's quirky sense of humor. "I didn't want anyone else hitting on me."

She reached out to her husband through her meat-obsessed alter ego, and soon they were exchanging heated messages. She was furious, and the next day she confronted him.

"You picked me up online," she recalls saying. "You're clearly still dating online."

"You think I didn't know that was you?" her husband responded.

She believed him. They stayed together.

"He was pretty convincing," she said. "He said, 'Cuts of meat? COME ON.'"

Related:

• Love Letters: She doesn't regret the affair

• The perils of online dating when you're over 40

• Anonymity hampers online dating

• The state of extramarital affairs