The dilemma I’m writing because my partner of seven years told me that he lost his virginity to a sex worker as a late teen while away with the army. He said he felt pressured by a so-called friend to do this and didn’t want to be the only virgin. I was shocked, because he’d always told me he’d lost his virginity to his first girlfriend. He insisted a condom was used, but I insisted he was tested for STIs, which he agreed to at the time.

During the following days he was passive about this, then annoyed and quite rude, which made it seem like a false promise. He behaved this way because he was scared of being tested, but it didn’t make it OK or put me at ease. I then found a service where tests can be ordered online, so we have both been tested and await results.

I feel confused and sad that he could treat a woman this way. I can understand why he lied about how he lost his virginity, but I don’t know if we would still be together if he’d told me the truth in the beginning. The thought of him with a sex worker is repulsive to me. That, together with having to take an STI test, makes me feel very turned off from sex and intimacy.

Mariella replies That’s perfectly understandable. There’s nothing sexy about sexually transmitted disease so it’s very sensible of you to insist on a test. Hopefully it will simply be a precautionary measure as, apart from a couple of less likely conditions, seven years would be an extremely long time for an entirely symptomless incubation. It seems to me, based on your letter, that the disease that might have been transmitted is mental rather than physical, judging by the paranoia and lack of trust you’re displaying. It’s not uncommon to harbour secrets from our past. Our post-Freudian society is all about expressing our darkest fears, but sometimes leaving territory undisturbed works equally well. So long as the only harm, if there is any, is to ourselves, I’d argue that we have a right to keep close to our chests whatever we choose, including less savoury behaviour.

Hooking up with another person doesn’t give you the right to download and judge their past actions. You have to meet them in the present and make your choice about them based on the person they’ve become. It’s irrational to expect your lover to give you full disclosure and then wait in trepidation to see if his past misdemeanours match up to your exacting standards. I know only too well how hard it is when you are young and your emotions override your ability for rational thought to put sensible distance between the present and the past. It can equally be a struggle to accept there will be relationships and moments in a lover’s life that still have resonance, good or bad, but that didn’t involve you. Part of growing up is about learning to display tolerance, empathy and understanding – qualities that can be hard to tap into during our more impetuous years, as anyone who’s tried to reason with a hormonal teenager will know. We are all flawed creatures leading the best lives we can, often against considerable odds.

He was an isolated teenager under pressure from a peer

It’s important to accept that little of what we feel and even experience is unique, but how we disseminate and gain wisdom from our encounters is of vital importance. I’m puzzled by the intense anger this revelation seems to have evoked in you, especially when you declare that had your boyfriend told you earlier, you probably wouldn’t be together now. It’s hardly an enticing invitation for confession. Would it have been better if he’d boasted about the encounter when you first met? Or revealed it with no sense of shame over an early dinner date?

What’s apparent is that your boyfriend is ashamed and uncomfortable about this incident and that seems more than enough of an indication of the person he’s become. He’s clear about his regrets, while you seem caught up in a muddle of emotions. I understand your sadness that he could treat a woman in this way, but he was an isolated teenager under pressure from a peer. What’s the big deal? You don’t need to feel disgust at your partner. In youth we leap far too easily to judgment and live in a world where shades of any hue are rarely tolerated. Offering simple understanding of both the sex worker and your boyfriend’s predicaments at the time would be a better way to deal with this.

If your relationship is founded on such a tenuous connection that a historical sexual encounter, apparently made under duress and regretted ever since, is reason to call off the affair, then perhaps the take-away from this is that your roots are too unstable to endure. There’s a curious misapprehension that coupling up gives us ownership over a lover’s past and a right to judge their actions as though they were committing them in the present. Personally, I’d be quite relieved that it took your man this long to come clean. It suggests that he’s not proud of his behaviour and has tried to leave it as far behind him as he possibly can. If you can’t forgive him, you must certainly move on, but I don’t consider his behaviour unforgivable.

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