It’s 5.41pm, and I am worried. My boyfriend usually calls me on the dot of 5.30, and during these unusual times, I crave this daily check-in. The thing is, I can’t call him. Leo is married and in lockdown with his wife and two children. It was hard enough being a mistress (a terrible 17th-century word, but nothing else quite fits) in “peace time”, but Covid-19 has given our relationship a whole new dimension.

Leo and I are both writers. We met at a literary festival last June. I am 51, a newly divorced Londoner, with a daughter at university. Leo is 49 and lives near Manchester. I knew from the outset that he was married: he wasn’t wearing a ring, but one of our first conversations was about family holidays. I wouldn’t say it was love at first sight, but he was funny and clever. Nice-looking, yes, but it was more his personality that attracted me; he radiated humorous warmth.

Knowing and respecting the rules (married men are off limits), I said goodbye to Leo and got into my car. But two days later, I was pleased to receive a Facebook message. Witty texts led to WhatsApp and, finally, a phone call. Soon we were speaking twice a day, often for hours – his wife has a corporate office job, Leo works from home – and he wanted to meet again. I put him off a few times, but we both knew it was going to happen eventually.

In November, we had a passionate reunion in London. Yes, we had sex – the first time I had slept with anyone since the end of my marriage. My nervousness soon evaporated and it was lovely. Mostly, we laughed and talked.

Leo never says anything negative about his wife. He insists she is “a good person”, but they have been together since they were 16 and complacency has set in. He feels taken for granted, and they are no longer physically intimate. Any concerns that he wanted me just for sex soon dissolved. Leo is an attractive and successful writer; if he was after a fling, he could have found one nearer his own part of the country, surely. I don’t feel great about adultery. It isn’t sisterly – and Leo’s wife sounds nice. On the other hand, I don’t feel guilty. I haven’t met her, and he says she has repeatedly ignored his requests to go to couples therapy.

What would you do if you met the partner of your dreams languishing in a marriage past its shelf life?

In winter and early spring, Leo and I enjoyed several rendezvous, weekends away, even four days in France. When we knew coronavirus was coming to the UK, we sneaked in a last tryst in the Lake District. It was very intense, very loving.

We have talked several times about the future. Leo is the main carer for his teenage children, and from the start told me they were his priority. So we are planning a life together after his younger child leaves home, in about four years’ time. This makes me respect and love him more. I can wait: I am busy with work, friends, my daughter. I know some people will roll their eyes, but Leo tells me his marriage is over and I have chosen to believe him. To critics, I would say: what would you do if you met the partner of your dreams, languishing in a marriage past its shelf life?

These days, the only time we can talk on the phone is when Leo goes for a run – and there is a limit to the number of runs a person is allowed. But these daily conversations are a lifeline. He will stop somewhere quiet, panting from the exercise. After four weeks in lockdown, Leo tells me his relationship with his wife has deteriorated further. (I don’t take pleasure in this.) She is, understandably, anxious and needy. The kids have cabin fever. He is the chef and chief “cheerer-upper”, but this has become wearing.

Facebook Twitter Pinterest ‘He will stop somewhere quiet to talk to me in the street.’ Illustration: Gym Class/The Guardian

Less burdened with family responsibility, I try to make him laugh, and it isn’t long before he makes me laugh, too. There is less intimacy (he is calling on a suburban street, after all). Instead we show our love through psychological support and fantasies about our eventual reunion. As for the virus, Leo is a healthy man in his late 40s. But I do worry; if he became ill, I have no idea how I would find out – except from the radio silence. I don’t know his landline number or his address; I have met only one of his male friends. If the very worst happened, I would be that mysterious woman you see in the movies, lurking at the back of a graveyard with big sunglasses and a black trenchcoat. (This is what happens when a person with an overactive imagination goes into lockdown.)

The toughest thing is the sense of powerlessness that comes with most of our communication flowing only one way. Anxiety aside, I am an impatient person who doesn’t enjoy waiting. Today, when Leo finally calls just before 6pm, any irritation evaporates – partly in relief, partly in empathy.

The question is: do I want to keep putting myself through this? And who knows how things will be when we get back to normal. My philosophy is this: if things don’t work out between us, I will be very upset, but not destroyed. My corona affair has taught me that I can love again after a horrible marriage breakup – and be loved again in return.

• Names and details have been changed.