Everything changed when I walked into a bar in Manhattan, where I had moved after six years living and working in London, and ran into James, an engaging 51-year-old CEO from Boston.
Over the next hour, I had what was perhaps the most intense discussion of my life and experienced an emotion that went way beyond attraction. I felt like I had found home - with a complete stranger.
But euphoria quickly turned to despair when he signalled the barman for another round, and I caught the flash of his wedding ring.
In an era when acceptance of sexually alternative lifestyles is on the rise, for the majority of people, infidelity is still a deal-breaker.
So Prue Leith, the chef, courted controversy this week when she challenged conventional wisdom by saying that her affair helped further her extremely successful career by giving her freedom to work long hours.
Contrary to the traditional hand-wringing narrative, Prue's part-time Prince Charming eventually gave her a fairy-tale ending. She married Rayne Kruger when she was 34, they had two children and lived happily together for 28 years until his death in 2002.
Everyone knows that being unfaithful can wreck marriages and lives. Indeed, the first time that James kissed me, I had a moment of deja vu - not of dating, but of driving; specifically, a collision I had as a teenager - and it hit me that there is a reason why illicit encounters are often compared to car crashes.
I went home alone that night, but I could not get James out of my mind. My heart wanted what it wanted; my head told me that using Woody Allen's logic to justify my position meant I was in even worse shape than I thought.
I felt guilt about his wife and two young daughters, because I have nursed friends and family through the soul-crushing grief and destroyed confidence after a partner strayed. Could I really handle the emotional casualties... especially if they were of my own creation?
When James called the next day, I told him honestly that I would never be satisfied with just an affair. He agreed, and didn't bombard me with clichés about his wife not understanding him - he simply said that neither of them had been happy for a long time, and he was making some major life changes.
He knew that the timing wasn't ideal, but he had felt a real connection and wanted to see me again. I knew it was wrong and yet it felt right. I'm not alone: statistics show that we are hypocrites when it comes to adultery.
Results from the most recent UK National Survey of Sexual Attitudes and Lifestyle showed that 63 per cent of men and 70 per cent of women disapproved of non-exclusivity in marriage - while nearly as many (60 and 45 per cent, respectively) confess to having practised it.
Over the following weeks, I tried to get James out of my mind. I told myself that soulmates, like unicorns, were figments of the imagination. I knew that, even in a best-case scenario, we faced an uphill battle.
Brad Pitt and Angelina Jolie (who, 10 years and six children later, are still inextricably linked to Jennifer Aniston in the tabloids), Prince Charles and Camilla, and Sting and Trudie Styler attract criticism even now for having relationships while at least one party was married. What hope did we have?
Once I stopped freaking out, I was surprised to discover that, actually, our odds were better than I thought. Another widely touted statistic says that only 2 per cent of relationships that begin in infidelity survive. But experts say that this may depend largely on how the affair started, and that a so-called "exit affair"- one in which the person cheating is already on the way out of the primary relationship - has a much better chance of ending in long-term happiness than one in which they are simply bored or a serial cheater.
When I dug deeper, I was surprised to discover that many of the happiest couples I knew had experienced relationship "overlap".
But admitting that their happiness came at the expense of someone else's heartbreak feels tacky, so they don't discuss it.
"We both just knew really quickly that this was different," my girlfriend "P" says of her husband and father of her son, whom she met when he was living with his girlfriend several years ago. "I felt horrible at the time, and I remember making comments about Daniel Craig being a dog for living with Satsuki [Mitchell] for years, then leaving her and marrying Rachel Weisz so quickly. I never would have believed it, until it happened to me."
As the recent Ashley Madison hack proved, disapproving of infidelity doesn't preclude huge numbers from doing it anyway, and some of my social circle have privately admitted to straying.
"I get a call from my married sex buddy about twice a month, because she knows that she can be in and out of my house in 45 minutes," one male friend told me.
"She says she and her husband have been living separate lives for years now, but she doesn't want to lose the whole setup: the house, two kids."
Another neighbour, who has been married for 16 years, sums up the rules of his and his wife's "don't ask, don't tell" policy: "Always use protection, never mess with anyone who my wife knows, and never hook up in my own house, because that would be disrespectful," he says.
In my defence, James told me that he had been planning to leave his wife with or without me in his life. But the truth is that I saw him again because I was selfish: I sensed that I had a shot at once-in-a-lifetime love and didn't want to let it slip through my fingers.
Though we still live in different cities and I don't know how the story will end, I have no regrets.
Happy couples who come together under illicit circumstances may never get to tell the cute "how we met" story. But perhaps their real secret is that high stakes forced them to ask tough questions early on, allowing them to construct a meaningful future together.
Or, of course, those who got together amid the breakdown of another relationship may just be a better match.
Which brings me to the final fear of anyone whose relationship began as an affair: what if another, even better, match comes along? Is it true that, as my grandmother used to say: "If they'll do it with you, they'll do it to you?"
I've long since learnt that love and life can spin out of control, no matter how carefully you have prepared. The only answer is to take nothing - and no one - for granted, and enjoy the ride while it lasts.
- Some names have been changed.
Catherine Townsend is the author of Sleeping Around and Breaking the Rules; lovedetective.com
