You are being naive if you think having sex only once with someone else will be the end of it, says Annalisa Barbieri

I’m in a relationship of 11 years with a man I met when I was 17. We have had many good, fun-filled years and I am still very much in love. He was my first boyfriend, first love, and first and only lover. We are to be married by the end of the year, which is everything I’ve wanted, but I’ve suddenly found myself filled with a sense of loss for my lack of experience outside our relationship. I’ve never even really kissed another man: we got together just as I was beginning to find myself. And, while we have grown and explored together as a couple, I can’t help but feel I’ve missed out on a lot of life experience. Is it possible to grieve for a life I’ve not had? I recently started talking to a man I met online, and while I have no desire for an emotional relationship with him, I am overwhelmed by a need to have a one-time fling to get it out of my system. We seem to connect with our sexual desires (I’m into BDSM, and my current partner is not) and I know it would be amazing. I’m so conflicted: please help.

You’re conflicted because there is something deep within you that you are denying. That doesn’t make your relationship bad or wrong, and it doesn’t lay waste to the past 11 years. But, I imagine, like a lot of people who started relationships when they were very young, you’re realising you might not be the same person you were when you embarked on it. I suspect you’re making this all about sex because it feels useful to compartmentalise it, but I think it’s about more than that. Very few of us end our 20s as the same person we were when they began: it is a decade of immense growth.

A lot does sound good in your relationship, but how did you feel when your partner proposed? Did you feel delighted or panicked? Nothing crystallises your emotions like the prospect of spending the rest of your life with someone. And, yes, it is possible to miss what you haven’t had, but grief is a strong word to use. There was another poignant phrase in your letter: “Just as I was beginning to find myself.”

Geoff Lamb is a psychotherapist who has decades of experience working with couples. “One thing that is clear,” he said, “is that you have to have a conversation with your fiance.” He thought that having a fling would not work. “If there’s that strong an urge inside you, then it won’t go away like that and, if you do this behind his back, you are planting a time bomb in your relationship.”

You are being naive if you think that having sex only once with someone else will be the end of it. If it goes badly, it will leave you feeling wretched, and you will start your marriage under a cloud of deceit. If it goes well, it will be hard to stop.

Lamb explained that we often have quite turbulent relationships in our teens/early 20s and, although they can be angst ridden, we also discover who we are and what we like. I don’t think you’ve done this. I know you don’t want to confront this, that you want everything to be nice, and that you love your fiance. But think carefully about getting married when you feel this way: you owe it to both of you to be honest.

I asked Lamb how you might start the conversation (we both agreed it was best to keep the online relationship private) and he suggested something like: “Look, we’re planning our wedding and I’ve got some concerns I’d like to talk to you about. We’ve only ever been with each other – how do you feel about that?” And take it from there.

You could even suggest going to couples therapy if you feel you could be more open there. “It might actually be quite liberating to talk,” Lamb said. “You can have an open conversation but don’t have to mention everything.”

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I wondered how much you were defined by this relationship. I can imagine your lives are probably very enmeshed if you’ve been together for so long, and that must make this even more difficult for you to get some perspective. You said, “This is everything I’ve ever wanted.” But it’s not, is it? Your relationship may survive this and you may grow together over it, but you cannot realise this without talking about it. Will it be easy to have this conversation, knowing what it might bring? No. But imagine living a life burying who you really are. We’re not living in the 1950s any more; you don’t have to marry your first love. Be brave.

• Send your problem to annalisa.barbieri@mac.com. Annalisa regrets she cannot enter into personal correspondence.

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