Walking into a sex party at a luxury penthouse in London, Sarah Tilley felt amazing. She had bought new underwear, had her nails done, and was wearing a fitted black dress. The mother of two didn’t know what to expect, but after her children had left home and her 17-year marriage had ended, she knew she wanted to experiment.

“I walked into the room and there was an orgy going on,” Tilley, now 53, remembers of that night in 2014. “The atmosphere – I’ll never forget it. It was this hum of groans.” She pauses, lost in the reverie. “It was fantastic.” There were no nerves. “I took to it like a duck to water,” Tilley says. “Like I’d been waiting for it my whole life.”

Tilley is not alone in having felt this way. She is one of a number of single parents exploring their sexuality after their children have flown the nest, with uninterrupted evenings stretching before them once more.

It is the situation at the heart of the new HBO comedy Mrs Fletcher, starring Kathryn Hahn as a divorcee who flings herself into dating and casual sex after her son leaves home. When your adult life has been subsumed into parenting, your children leaving home doesn’t feel like a nest emptying – it feels like freedom.

After Tilley’s marriage ended, she spent a period of time being celibate; she wanted a total reset. Her children were still shuttling between her house and her ex-husband’s, so she knew she needed to date outside the home.

When it was time to start dating, Tilley resolved to do things differently. She had grown up in a conservative household where talking about sex was discouraged. After meeting her ex-husband, she had brought up the possibility of an open relationship, but he had shut it down immediately.

HBO’s Mrs Fletcher features a divorcee (played by Kathryn Hahn, left) who explores dating and casual sex. Photograph: HBO

“I knew I was missing out on sex, but I put it to one side,” says Tilley. After the divorce, she chucked herself headlong into everything she had been missing – BDSM, group sex, sex with women and men – all the things she had wanted to try all those years, but couldn’t. It was glorious.

Tilley had a rule. She would meet someone and ask herself: do I want to have sex with this person? If the answer was yes, she would go for it. “I had a voracious sexual appetite and I was making up for lost time,” she says.

When Richard Paulssen’s wife died in 2014 after a long struggle with alcoholism, leaving him in sole charge of their 14-year-old daughter, dating was the last thing on his mind. “My mum said to me: ‘You’re still young, you’ll meet someone,’” says Paulssen, a 57-year-old building contractor from Houston, Texas. “I said: ‘I’m done. I don’t want a partner.’”

That changed in February 2018. Paulssen woke up one morning and felt different. For years, he had had recurring nightmares involving his late wife – he would try to convince her to go to rehab, but she would refuse. “They just stopped suddenly,” Paulssen says. “I realised I wanted to meet someone.” His daughter was going to college and the timing was right. Then Kirsten, a 50-year-old former makeup artist, came into his life. It was a revelation.

“Those volcanic feelings you have when you’re 16, the teenage angst and all the rest of it – it was the same,” says Paulssen. “I was so taken aback by it. I never expected to feel this way.” Predictably, the sex was great. “We have a really active sex life and thoroughly enjoy each other.”

For Lucy, a 46-year-old manager from Wales, it was her daughter who encouraged her to venture into BDSM. “She told me to dip my toe in,” Lucy says. “I’ve had a great time.” She discovered something unexpected about herself – she is a natural dominatrix. Now, she has casual encounters with people she meets through online kink communities. “I’m very open-minded,” Lucy says. “I’ll try anything. But I only play with people I like.”

The idea that people might find me attractive, even if it was only for the night, was amazing Holly, 50

Making up for lost time; exploring a side to your sexuality that was suppressed due to child-raising: it is a transformational time. But it is good to exercise caution, particularly if you are new to casual sex. “Be aware of yourself,” says the sex therapist Miranda Christophers. “What is it you want? What might you gain from these relationships? And how will you meet people?” She advises that people practise safe sex – STI rates increased by 9% among over-45s in the period 2012 to 2016.

If you are ready for it, a midlife sexual awakening can be wickedly good fun. “There are times that I look back at things and think: I can’t believe I did that,” laughs Holly, a 50-year-old university worker from London. A single mother, Holly didn’t start dating until her daughter left home.

One day stands out: Holly went on a date and woke up on Christmas Eve after a night of fun, casual sex. She went home and found another text – from a person she had been talking to online, asking if she was free. Holly invited him over. “The next day was Christmas and I went to see my family as if nothing had happened,” Holly chuckles.

An advantage of sexual exploration in later life is that, generally, you are less insecure. “I didn’t have the confidence to do this in my 20s,” says Lucy. “Whereas, in my 40s, I no longer care about what anyone thinks of me. I’m comfortable with my filthy mind. All the things I was suppressing, the people I play with find an asset.” For Holly, casual sex felt validating after years of celibacy. “The idea that people might find me attractive, even if it was only for the night, was amazing,” she says. “I went berserk.”

Sexual exploration in your 50s and 60s can be profoundly exciting, but also tinged with regret. “I’m grateful for my marriage, but it would have been amazing to be a young woman celebrating my sexuality,” says Tilley. “I am sad that didn’t happen.”

She is making up for lost time. After a few years exploring the alternative sexuality scene, Tilley is happily in a relationship with Boris, 14 years her junior. They are “monogamish”, meaning that they occasionally dabble with other people if the mood is right. “I’ve become something of a wonder piece to my married friends,” Tilley says.

It is not always a carefree sex fest – when you are plunging into the waters of internet dating, you are bound to encounter a few duds. “Inevitably, I met a few people who were awful,” Holly says. One man kept standing her up. “But mostly they were nice.”

To any single parents looking around their empty homes and thinking that a sex swing would do nicely in that spare bedroom, Christophers says go for it. “Focus on your needs and what you want, then take a step out there and do it.” Tilley now helps other people discover their sexual selves after child-raising and divorce. “Every middle-aged person should know that you don’t have to sign off at midlife,” she says.

Paulssen feels like he has been given a second act, which he never expected. “It’s like a brand-new chapter in my life has started,” he says. “I’m very happy with life in general.”

Some names have been changed