The dilemma I’m married to a wonderful man and we have three children, but I have a burning desire for someone else. I was on a girls’ weekend away when I met him, and the electricity and chemistry between us was out of this world. We had amazing sex and chatted about everything – it was as if we were soul mates. He also has a partner and two children and lives a couple of hours’ drive away.

He asked to see me again and gave me his number, so I made contact two weeks later (I couldn’t get him out of my head, having no appetite, not sleeping and no concentration). We’ve been texting, but now he’s cooling. It’s crazy how this has affected me. I’m crying a lot and can’t stop thinking about him. When I go to sleep he’s on my mind – and again when I wake in the morning. This is the first time in my marriage I’ve had my head turned. This guy really has got under my skin and I’m dying to see him again. I know I’m being greedy wanting both my husband and him, but is it possible for the heart to love more than one person? I’m going out of my mind.

Mariella replies You may well be! The heart is an expansive organ, but our lifestyles are generally less all-embracing. I’m certainly struggling to understand what it was about this recent escapade that spelled continuity to you. I totally get the enticement. An oasis of penalty-free sexual abandon rising up in the desert of domestic duties is hard to ignore. Given you have a husband, three kids and the demands of everyday life, it’s easy to see why, after a few cocktails, you grasped the opportunity for what’s erroneously described as “harmless fun”. But that’s where the fantasy ends. We both know that, in the real world, Newton’s third law applies: “For every action, there is an equal and opposite reaction” – a cautionary reminder of consequences.

The reality is that while you both appeared to be winners in the frenzied moment, the grim, grey light of dawn invariably reveals a loser. I know that women and men are now equal players on the sexual field, so it’s increasingly hard to generalise around gender, but in my experience as witness to many a tangled tryst, it’s hard to ignore the fact that, when it comes to the concept of free sex, it’s usually the woman who’s left out of pocket.

You are risking all for someone else’s unfaithful husband

You’re now facing up to the fact that there is no such thing as unfettered freedom when it comes to human coupling. There’s always someone left wanting more and, on this occasion, it’s you. That’s not to say you need to take this as a confidence-smashing body-blow. I’m sure your lover had an equally good time on the night, but for him the parameters haven’t changed. For you, they’ve widened so you want to include him in your life.

He seems to have placed your encounter in the box where he believes it belongs, while you’re letting it cause emotional havoc. If you’re going to have casual sex, you’ve got to accept the terms: you’ve no idea how many letters I get from people eager for a momentary escape who then let the experience turn their existence upside down.

You said it was “as if we were soul mates”, which brings me round to a topic that keeps coming up, no matter what the dilemma – our incapacity as a species to know when we’ve got enough and to settle for it. The man you’re setting your heart on, following your very brief encounter, is somebody else’s unfaithful husband. Even if he wanted to continue your sexual foray into a full-blown affair, is that really the sort of person you want to risk everything for?

I’m a bit long in the tooth to accept the notion of people being “soul mates” simply because they chit-chat between orgasms on a night of unbridled lust. It’s not often you turn to Monty Python for emotional insight, but I feel it’s my responsibility to spell out in no uncertain terms – as expressed by Terry Jones in the Life of Brian – that this guy is “Not the Messiah, he’s a very naughty boy!”

What does deserve further contemplation is what deep-rooted desire he’s fulfilling in your otherwise contented relationship, aside from the obvious. No partnership can supply our every need, so we all look beyond our relationships for the missing elements, whether it’s something as frivolous as dancing or as serious as political debate. The problem arises when the things we deem ourselves to be short-changed on mean risking the fundamental building blocks of our relationship – in this instance, trust and fidelity.

You asked the question, so I’ll answer it: as you rightly suspect there is little hope of successfully expanding your family boundaries to include this man and the sexual frisson that he represents, unless you’re prepared to risk all. You’ve had your night of passion and proved to yourself you can still rise to those heights of abandon but, back down on solid ground, you have kids, a husband and therefore a family. When you look at what you have to lose, and compare it to what you’d gain, the choice from where I’m sitting seems pretty clear.

If you have a dilemma, send a brief email to mariella.frostrup@observer.co.uk. Follow her on Twitter @mariellaf1

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• This article was amended on 5 January 2020. As readers have pointed out, it was Terry Jones not Eric Idle who said, “Not the Messiah, he’s a very naughty boy!”. This has been corrected.