It’s a beautiful day in Barcelona. The sun is high like a gold coin tossed into the blue sky and the coffee and pastries on La Rambla are good. Meanwhile, my wife is grafting more than 700 miles away in cold, grey London. But she sends me a cute text (“Call that work? Enjoy it, you lucky *****”), the sort of peppy message that keeps a mature, trusting marriage going.

Life couldn’t really be better. Or could it? It turns out it could. Much better. All I need is to arrange to have rampant cheat sex with an online hook-up in the certain knowledge I will never get caught.

“Everyone would do it if they knew for certain there wouldn’t be consequences,” says a voice in my head.

Except the voice isn’t in my head. It’s what the bald Spanish guy sitting opposite me is saying. His name is Albert Arnaiz and he is offering to coach me in how to have an affair with zero chance of discovery.

“Do it,” he encourages. “You will learn so much about who you really are — become a better version of yourself. This is the modern world — in the digital age no one settles for one person anymore. You only have one life. Live it.”

Arnaiz’s seven-step “method” to cheating is elucidated in his book, Shicret. It stands for Secrecy, Hearing, Intimating, Cohabiting (how to live alongside the person you are deceiving), Reiterating (cheating over and over again), Evading and Terminating. It’s an extraordinarily saucy manual for the duplicitous shagger. Arnaiz has obviously put a lot of work into it.

“I have had the most incredible sex life,” he informs me. “The adrenaline! The adventure! I don’t recommend it for people who get anxious easily, but for everyone else — eat from the feast!”

Arnaiz and I are sitting at a pavement café in central Barcelona. There are beautiful Spanish women at every table and Arnaiz, a handsome, eye-catching dresser, is already attracting sideways glances. But is it the salmon-colored sports jacket that would put him straight into contention for a Miami Vice remake or the fact that he very earnestly and loudly admits to having had sex in a cinema?

“Mostly I have enjoyed digital infidelities — partners I find on a site,” he explains. “But some of the most pleasurable are analog encounters: you meet someone in a bar and it’s, ‘There’s a movie starting in ten minutes — let’s go!’ ”

It’s an extraordinarily saucy manual for the duplicitous shagger. Arnaiz has obviously put a lot of work into it.

Arnaiz is 43. He is in a committed relationship and has a six-year-old daughter, but this stability is quite new. Born in Barcelona, he was 17 when he had his first girlfriend. That relationship lasted two years and he was faithful. However, after that he was in a long-term relationship that lasted 13 years. He cheated. A lot.

“Maybe 100 times in 3 or 4 years,” he claims. “It was like a drug for me. I don’t believe in marriage and the term ‘love-making’ doesn’t convince me. I prefer to call it f***ing.”

His current relationship began with infidelity. Both he and his partner cheated after meeting on a website for people wanting an affair. Has his partner read Shicret?

“Yes. She thinks I’m crazy but she is trying to be supportive.”

Are your cheating days over?

“Who knows?”

Inevitably, there is an accompanying podcast, Tu Profesor Infiel (Catalan for “Your professor of infidelity”). I get coffee all down my front when he tells me that in real life he is a college lecturer. He teaches marketing at two places in the city.

“Most of my students know about my book,” he smiles. “It’s funny to see how they regard me in the class sometimes.”

What about the college principal?

“I’m not sure. I don’t talk too much about it with her.”

In Spain, Shicret has caused quite a stir and Arnaiz has dutifully toured the talk-show sofas. The reason his manifesto for cheating resonates, he claims, is that there is a boom in female infidelity.

“Globally, 40 percent more women are unfaithful than 35 years ago,” he says. “They are better at it. They are cooler and less clumsy than men about keeping secrets. And we now know that the last year of each decade from the age of 29 — so 29, 39, all the way to 69 — is when people most want to have an affair.”

In the UK, he says, 34 percent of men and women would cheat if they could be sure of not getting caught. In France the figure is 47 percent. In Brazil they don’t seem to be able to keep their pants on—according to Arnaiz, 80 percent of the population have already cheated with someone else.

Which brings us to the UK’s problem with sex.

“I have never had sex with a British woman, but I think that you and others from northern Europe are not so comfortable with the idea of cheating. Except the rich and powerful ones, of course.”

What does he mean?

“The rich and the powerful in your country have always done as they please. Look at your king—he is on the throne with a woman he had an affair with. And Boris Johnson. A man greedy for women. But the digital age is making desire available to everyone, so I believe you will learn to take more chances.”

Spanish people might be more relaxed about infidelity, he says, but sometimes they are still shocked by the most egregious cases. Six miles west of where we are sitting is the upscale Esplugues de Llobregat area. And there is the five-story mansion where, until recently, the Colombian pop star Shakira and former Barcelona player Gerard Piqué lived with their two sons, Milan, 11, and Sasha, 9.

That is until Shakira allegedly discovered Piqué, 37, was having an affair with a woman 12 years his junior called Clara Chia Marti. Shakira is a global sex symbol. Chia Marti was an intern at an events company Piqué owns.

The Shakira/Piqué case gets to the crux of it for Arnaiz. He doesn’t have a problem with Piqué cheating, but he is outraged because he reportedly got caught.

“Never bring a lover to the house! Never! It’s in my rules [it’s listed in a section called Places to F*** Around]. You have to find another place. A car! A forest! A bathroom!”

There’s a strange morality at work here. Arnaiz is also very angry on Shakira’s behalf because of the way Piqué’s alleged affair was apparently discovered.

“Many people in Spain like me think Piqué is a bastard because not only did he let another woman into the family home, but Shakira faced the pain of discovering this infidelity when she saw food had gone missing from her kitchen.”

I guess Shakira found out the hard way: chips don’t lie. Or in this case, apparently, it was strawberry jam, which Chia Marti ate from her fridge. (In the video for her 2022 song “Te Felicito,” Shakira included a scene involving a fridge, but replaced the jam with a severed human head.)

“This eating of the victim’s food is unacceptable,” says Arnaiz. “The whole reason you cheat but don’t get caught is so that nobody faces pain. Piqué didn’t take care of this.”

OK, I’m not going to have an affair. But I guess it can’t hurt to know a little more about how it all works. Arnaiz laughs when I say this. “Yes, a lot of people are buying my book because they want to check the signs their partner is not f***ing another one,” he says.

First things first. Don’t buy a hard copy of his book—read it on a tablet and keep the password secure. And don’t get caught looking for partners on Tinder or Hinge—use dedicated cheat sites like Ashley Madison, the French cheating website specifically marketed to women called Gleeden (it’s free for female subscribers and, famously, has a “panic button” for exiting the site if suddenly disturbed) and married dating site Victoria Milan.

Arnaiz is similarly thorough with his advice on choosing someone to have an affair with. When you first call a prospective partner, focus on voice rhythm and tone—they might just be talking about the weather or their favorite film, but it should sound like they are already having sex with you. “They show being horny just by talking,” he says. “Same for you—be thinking what you would like to do to this person in the bedroom while speaking about ordinary things. They will hear those thoughts in your voice.”

Wow. I remember the first time I spoke to my wife, we talked about the fact that train tickets from Bristol to London were cheaper if you changed at Didcot Parkway.

When you find someone to cheat with, Arnaiz is also scornful of what he calls “micro-infidelities”, such as sending a saucy text or photo. Meet them and have sex for real. He gets quite passionate about this. In fact he does that thing that modern politicians do: casting himself as the little guy fighting back against an implacable establishment blob.

“It’s terrible how big tech has made infidelity so virtual. What are they doing to us? We need to stop browsing and cross the boundary to real intimacy or what have we become?” It’s crucial, he argues, to manage your guilt. The “relationship self” and the “unfaithful self” must co-exist. “Guilt will pass,” he says. “But your long-term partner knows you better than anyone, so you must skilfully manage your eye contact, your breathing and even your perspiration. All that is part of the skill—to remain cool and evade capture. And, you know, it’s part of the excitement.”

Arnaiz was born in Barcelona. His dad was a truck driver and his mother an administrator. His confidence is attractive. So are his big shiny teeth. I can imagine a lover feeding him apples from a flattened hand. But I’m just waiting to hear about the childhood trauma that made him such an incorrigible and duplicitous shagger. I wait in vain. There isn’t anything.

“I had a very normal upbringing,” he says. “But my family have made it clear they don’t like what I’m doing with this book, even though they respect that I have skills to teach.”

Those skills include tips on allaying a partner’s suspicions. For example, if you say you are going shopping and your partner becomes suspicious, throw them off the scent by actually going shopping.

He does that thing that modern politicians do: casting himself as the little guy fighting back against an implacable establishment blob.

That’s gaslighting, isn’t it?

“The point is, you are protecting them from this terrible feeling—jealousy.”

I notice that his book cover shows his middle name as “XL”. Mine is Charles and other people I know have middle names like Paul or Simon. Why is he called XL?

“Why do you think?”

Arnaiz has big feet and I see from his snug jeans that he dresses significantly to the left.

Shicret is making waves in Spain, and he was all over the TV on his American book tour in September. If the success continues, he aims to give up teaching and become an infidelity coach full-time. He already charges $1,100 for a short course.

“I have coached CEOs from big companies—they’re busy and they want to learn quickly how to have an affair, but also protect their reputations. These days, an affair can cost you a career you have spent years building. Not getting caught can be worth hundreds of thousands of euros.”

“My family have made it clear they don’t like what I’m doing with this book, even though they respect that I have skills to teach.”

The rewards are obvious. Although he says affairs occur due to waning emotional intimacy and boredom, the case studies in his book mostly speak of people popping the cork on massively repressed sexual desire. Having spent an afternoon with him, I have a suspicion these anonymous female case studies all involve him.

“Maybe,” he says. “Let me just tell you that it is usually a lie when people say they had an affair because they were emotionally unfulfilled. They wanted great sex. That’s the truth.”

While I am sipping my coffee and, I suppose, possibly looking a little skeptical, even judgmental, Arnaiz says I would make a good cheat. I get to spend time away from home, I like to chat and I have made him laugh (I told him, looks-wise, he reminds me of the Man City manager Pep Guardiola, the main difference being that Arnaiz only likes playing away from home).

“You’ve really never cheated?” he asks me. I take another sip of coffee and wipe away a creamy top-lip moustache.

Yes, actually, I did cheat once. I was in my early twenties and did the dirty on my first serious girlfriend. But hey, she cheated first. She went away for a weekend and came back acting all distant, saying the passion in our relationship was gone and, you know, there was a whole world out there to explore. It was an incredibly painful experience. I had never had a proper girlfriend before and felt so suburban and guileless. We struggled on, but the whole thing shook my confidence.

So when an opportunity presented itself, I took it. I discovered that, in relationship terms, I’d been on dial-up when there had been 5G internet all the time. I met someone who really liked me rather than just tolerated me. And forbidden sex can be very intense. There’s an old Stax song, “If Loving You Is Wrong (I Don’t Want to Be Right),” which totally captures the erotic charge of infidelity. And yet pretty soon guilt gnaws away at the soul. Being unfaithful really does hurt people. Arnaiz disagrees. He thinks it serves a higher purpose.

“Eighty percent of people who cheat still manage to save their relationship,” he says. “An affair can make you a bigger, happier person.” Easy for him to say. Has he ever been cheated on?

“If someone has cheated on me, they never told me,” he says. “But that’s life. I accept it might happen.”

The “t” in Shicret is for “termination.” You must end the affair. Arnaiz is quite prescriptive about this. The more intense, the quicker it should finish. If you are having sex every week, it should end after three months. If you only see each other once a month, you might survive a year.

“Ending it will reduce the chances of getting caught. Afterwards, you relax a while. You consider what you learned. Is this a frog or a prince, someone you want to be with longer? If no, then you can start again.”

And be warned, cheating is hard work. “Lying can be terribly exhausting. I recommend taking dietary supplements.”

He straightens the cuffs of his salmon-colored jacket and I have an uncomfortable thought: am I supping café con leche in the Barcelona sun with a stone-cold psychopath?

I ask Arnaiz this straight out. He throws his head back, laughing.

“You are not the first to say this,” he says. “I don’t think so. But you only have one life. When you get old you will only remember the opportunities you didn’t take.”

Michael Odell is an interviewer and features writer