Every night for several years, a happily married entrepreneur would have sex with his wife, wait for her to fall asleep and sneak out of bed to visit prostitutes. He showered his favorite escorts with extravagant gifts — bankrupting the family business — only to abandon them as soon as they confessed their feelings. Another man, a middle-aged academic, liked to put on mesh costumes and masturbate in front of the mirror, but avoided having sex with his boyfriend. Meanwhile, a soft-spoken paralegal went to the dentist for a tooth extraction, looked up at her doctor and fell madly in love. He swore he did not reciprocate, but his patient did not mind: She loitered outside his office, followed him home, clipped news stories that bore his name and built a shrine for objects he had touched.

In “The Incurable Romantic: And Other Tales of Madness and Desire,” British psychologist Frank Tallis gives readers a peek inside the therapist’s office and a sense of how otherwise reasonable people can go crazy over love. Many of the “symptoms” of ordinary desire, Tallis notes, mimic the symptoms of mental illness: recklessness, agitation, irrational behavior. “Love sickness was considered a legitimate diagnosis from classical times to the eighteenth century,” he writes.

Even if we no longer recognize love as a disorder, we cannot deny its power to destabilize and distort. Tallis estimates  sexual jealousy and rejection motivate up to 10 percent of murders as well as a significant number of suicides. The stakes of romance are high: We celebrate love as all-important, even as the meaning of life. “In the modern world, we’ve lost faith in God and spirituality, but we still have faith in love and particularly romance,” Tallis says in an interview. “It has, for many people, a kind of redeeming quality. I think that often love and sex are surrogates for the kind of things that spirituality provided.”

Yet, in Tallis’s own practice, he noticed patients were reluctant to confide their romantic troubles. “People come in and are embarrassed about talking about this kind of problem,” he says. “Love itself, they regard as something that perhaps is adolescent.”

With his new book, Tallis — who is also the author of a series of crime novels set in Sigmund Freud’s Vienna — hopes to show love gone wrong is a valid source of psychic distress and deserves to be treated as such. “We have sex education,” Tallis says. “It would be a good idea if we had love education as well.” In the eight years he spent training to become a clinical psychologist, Tallis says he attended only a single, hour-long lecture on love.

His book explores the sometimes-fuzzy line between the kind of love we hold dear and the kind we condemn as dangerous, even illegal. (One of Tallis’s patients is a self-loathing pedophile who promises he has never acted on his fantasies but does not trust himself around his friend’s 8-year-old daughter.)

Many of our notions about romance are “semi-delusional,” according to Tallis. “One of the main beliefs to do with romanticism is the idea that there is a single person who we are fated to meet, and it’s in the stars. Even rational people subscribe to this belief. If you really believed that, then if a relationship doesn’t work out — if ‘The One’ proves to be unsatisfactory — then you are bereft, and there are no other opportunities.”

Clinging too tightly to expectations about fate and “The One” can leave us susceptible to the kind of madness that plagued Tallis’s most lovesick patients. “In some individuals, these beliefs are more rigidly held, so those individuals would be more vulnerable to pathologies of love.”

Online dating may help puncture some of those ideas: With an almost endless string of profiles at our fingertips, the notion of The One is harder to believe. Apps also empower users to take control of their destiny — chipping away at fate’s role in the dating process. “We don’t just hang around in clubs and discos waiting by chance to meet someone. There’s an enabling aspect of modern dating technology whereby people can study profiles and match themselves up.”

Apps, ironically, may be restoring a more traditional approach to dating. “The Internet and dating apps replicate some of what arranged marriages used to do. The idea that you had a matchmaker who would try to match up the couple in terms of their personality characteristics, their beliefs, what they wanted in life — in a certain way, dating apps do the same thing now. If you think about some of these ancient ritualistic societies and modern society, in some ways they’re not so different.”

And even if certain apps can facilitate casual hookups, Tallis sees many online daters following a more old-fashioned trajectory. “There’s texting, and then there’s a phone call and then there’s maybe a date — it’s a slow approach to the possibility of physical intimacy.” He sees this as a positive development. “Sex isn’t as casual or as innocent as we generally kid ourselves. When you have sex with someone, your perception changes. It’s very likely you’ll see your partner as more attractive than they actually are. You’ll feel more attached to them. If we have a sexual connection too early, that biases our opinion positively before we’ve had time to decide even whether we really like that person.”

Tinder is often blamed for killing romance. But given how easily the pursuit of “The One” can veer into stalking and violence, perhaps it is time for romance to get taken down a notch.