It is the latest revival from the carefree early 00s to brave the fire-scorched hellscape of the 21st century. The relationship between Ben Affleck and Jennifer Lopez, AKA Bennifer, has roared back with a vengeance, with Lopez announcing their re-engagement this month, almost 19 years after they called off their wedding.

When we talk about a couple’s chemistry, we usually mean something about sex. It is more literal with Affleck and Lopez, who create a compound that is far more compelling than Affleck or Lopez as single atoms.

Here is a precis for those who weren’t alive or paying attention two decades ago. The couple met in 2001, while filming the universally panned romcom Gigli. Their subsequent romance led to Bennifer being defined on Urban Dictionary as “an attractive couple that have money, fame and beauty yet are still universally hated” and a “combination of two things that separately suck but when put together can achieve a level of sucking not understood by physics”.

But that was just how the cool kids saw it. To the mainstream media, the pairing was blessed, recalls Marie O’Riordan, who was then the editor of the lifestyle magazine Elle. When two extremely famous people fall in love, “the story takes on its own momentum”, she says. “‘Will they break up?’ ‘Oh, they’ve got engaged?’ ‘What are they wearing?’ ‘Where’s the wedding going to be?’ It all plays out in front of you.”

Perhaps in response to the pitiless scrutiny of their engagement – performed to an unblinking audience, like Cinderella in a carriage of glass – they went a bit bonkers. Affleck popped the question in late 2002 with an engagement ring that was reported to cost $2.5m; Lopez called it “the most magnificent thing I’ve ever seen”. (She didn’t actually finalise her divorce from her previous husband until 2003, but it is not bigamy if you only get engaged.)

In 2003, they postponed their wedding “due to the excessive media attention”. By 2004, they had split up. She married Marc Anthony that June to become Anthopez, while Affleck married Jennifer Garner in 2005 to become Affgar. Neither of those titles took, but the relationships lasted well into the 10s.

***

‘Excessive media attention” is a bit of a red herring. It is possible that the real problem was our general overinvestment in the romance, as with Posh and Becks (married 1999, still together) and Jennifer Aniston and Brad Pitt (married 2000, divorced 2005). When everyone is wishing so hard upon a pair of stars, it must be hard to tell which feelings are real and permanent and which have been generated by the crowd.

O’Riordan was at Lopez’s second wedding, in Lake Como in 2001, to the dancer Cris Judd. “Quite a lot of the senior British press were invited and we were all dancing round the top table, going: ‘But they don’t even know me.’ They didn’t even look happy.”

When a couple is kiboshed by a context they can’t control, there may still be life left in the relationship. But is it a good idea to return to an old flame? How do you know whether you are rekindling something genuine or splashing around the lighter fluid of your life’s disappointment in an effort to reanimate something long since expired?

Susanna Abse has been a marriage counsellor for decades and is releasing a book on the subject, Tell Me the Truth About Love, next month. She has never seen one of these back-together couples professionally. “That’s an interesting thing in itself,” she says. “They’re not a very large demographic going to couples’ therapy.” But there is a richness to a shared history that we all instinctively understand, she says. “I once did a lecture series on intimacy and I had pictures of different kinds of couples – a couple in a sexual embrace, couples in families with their children, then older couples, laughing with each other. I asked people what they thought was the most intimate picture. It clearly wasn’t the sexual picture; it was this couple laughing together. That sense: ‘We shared something. We know each other. We have a special “in”. I can stretch all the way back to the essential you.’”

This feeling can be amplified if the first time you got together was also the first time you fell in love. Details will have etched themselves into your memory, making that person part of your identity for ever, regardless of whether you have maintained a friendship.

Aled, 53, and Jem, 49, got back together in 2014 after meeting in 1995, when they had a blissful year of freedom, hitchhiking up and down the UK, going to gigs and festivals, at one point following Patti Smith to every date she played in the country. “It was one of those moments of illumination,” says Jem. “We were at the last Patti Smith gig in London and he’d gone off for a little bit and came back with a backstage pass, but there was only one. And I thought: ‘Shit. I love him so much that I want him to have it. Because it means so much to him. I can just wait in the bar.’ I was quite surprised at myself – I was only 22 and I was being quite mature. Then he grinned and held up a second pass.”

Often, if you don’t remember things the same way, it adds texture to the memory. “There was a really bright, effervescent, easy feeling about being around each other,” Aled says. Jem disagrees: “It wasn’t easy at all. I felt absolutely tongue‑tied. I thought you were just so cool.”

There can be a distinctive sweetness, a lack of consequence, to these memories. Abse says they “return you to a place, emotionally, prior to all the knocks and betrayals of life”.

Kate and Jamie Laverty, both 44, have been married for 13 years and have two children, but they first dated in 1994, when they were 16. “Jamie joined my friend’s terrible indie band. He came on stage and I said: ‘Who’s he? He’s not in the band,’ and he heard me. That was so embarrassing.” Only 16-year-olds are capable of that exquisite cringing over moments that are really not that embarrassing.

If celebrity relationships can crumble not because of incompatibility so much as the weight of public expectation, regular ones can fall apart simply because you don’t have much agency in that decade of transition – call it 15 to 25 – from childhood to adulthood. Jem was going back to art school and wasn’t looking to settle down; neither was Aled. Kate and Jamie talked about going to adjacent universities, but then she didn’t get into Manchester, he didn’t get into Oldham and nobody had a mobile phone. She says: “I was really excited about university and I thought it would be sad to be thinking about someone else and not being able to see them. I just thought it would be a rubbish experience. And I didn’t think we’d be married 25 years later.”

Love is wasted on the young, because they don’t know anything. It is like giving a baby a mango – how are they supposed to know it is any more exotic than an apple? “There was a bit of a failure to recognise how brilliant our connection was – how rare and how precious,” Aled agrees.

If what turns out to have been a really important relationship was discarded for a relatively trivial reason, you can try to pick it up again, but it is unlikely to be on friends-with-benefits terms. “I thought if we got back together it would be instantly a serious relationship,” says Kate. “You couldn’t casually date someone who was your first love 13 years earlier. And it was like that.”

Jamie got back in touch with her via Facebook. “It came over quite quickly that he was thinking about the past,” she says. “If someone in online dating had sent these messages to me, three messages in, that would have been a red flag. But because I already knew him so well …” He came over for dinner and they were pretty much engaged before she produced the noodles (well, within six months). “It definitely felt romantic, it definitely felt like this was meant to be: this person from my past has swept back into my life.”

Jem and Aled started messaging privately on Twitter when, Aled says, “we were both just out of relationships where we were not treated as well as we might have been”. They didn’t meet for months, as Jem was living abroad with two children, but they were messaging constantly, Jem remembers: “Once, we counted 200 messages in a day.” Aled adds: “It was so intense; I wasn’t sure you were real. I thought I might have a split personality and discover a second phone somewhere.”

They finally met when Jem came to England to visit him. “It was like a 90s romcom,” Aled says. “The PA in the airport was playing Be My Baby.” Jem adds: “It was very difficult to make eye contact at first. It’s like young love with the brakes off, because you know who you are.”

Aled says there was a “weird intensity to it”. “You’ve got all the fizz of new love that has really blossomed, but you’ve also got this deep, anchoring weight, the trust, the familiarity, the integrity of really knowing who that person is,” he says.

By the time they resumed their relationship, Jem was identifying as non-binary. “But I’d always known that – the only difference was that I now had a vocabulary and context for what I’d always felt,” they say. Aled adds: “It was more like: ‘Now there’s a name for that thing that’s always been true.’ It’s not like they’d converted to Christianity.”

Part of the instantaneous trust – which would probably be an illusion, a mirage or at least a punt in a regular love affair – is knowing the central pillars of each other’s lives, says Abse: “‘I know where you come from, I knew your mum and dad, I remember where you lived.’”

All of that is great, but now you have to see each other’s parents again for the first time since you were a kid – and maybe one of you (Jamie, say) used to have long hair and is now bald. “It was weird getting back together and seeing his family again, but his parents were so warm; I could do no wrong,” says Kate. “It didn’t hurt that his mum really didn’t like his ex. She wouldn’t even say her name – it was always ‘her’. And I was the reason he’d moved back nearer to them, rather than living in the Midlands with her.”

Jem’s dad, meanwhile, had leaned over to their mum in the middle of their first wedding and said: “It ought to be Aled,” but they found this out only when they got back together. “There was only one person who was surprised and that was an ex of both of ours,” Jem says.

A quick corrective, before this all becomes too panglossian: life changes don’t always make us better at relationships. “There’s always the quest for the new when you’re young,” Abse says. “Twenty years later, you might think: ‘I’ve had a look round – it’s really nice back home.’”

The flip side of this is that you may be set in your ways – as Carol found when she got back together with her former flame Steve in 2014. By this point, she had two children and “was definitely in love with him. I was mid-40s, thinking: ‘It would be lovely to have another baby.’” At this point in our video call, her 19-year-old daughter is making an internationally recognised hand signal for “crazy” behind her. “He was late 40s, had never had children and was completely freaked out by just how structured life with kids is; how much things have to be planned.”

When they were having their breakup chat, he raised an incident he had found problematic – when she hadn’t been able to go to a gig on the day of her daughter’s birthday party. “He was never going to get priority and, in good faith, he just didn’t understand that. I thought: ‘My God, if I’d known you didn’t understand that I had to be there for that, I would never have got into this.’”

Perhaps reunited couples who do work out are aware of how much could have gone wrong – they seem to be much more expressive in their gratitude to the universe. As J-Lo said recently, comparing this iteration of Bennifer with the one two decades ago: “There’s more of an appreciation and a celebration for it, which is nice. It was: ‘Oh wow, we’re not used to this and it’s really beautiful.’”

Jem says: “It doesn’t feel like we wasted time. I learned a lot. I made a load of mistakes. It’s made me who I am now, and who I am now is what I want to bring to the relationship.”

Aled says: “These days, I recognise love while it’s happening. I’m appreciative, I can see it. There is a conscious joy at the start and end of every day, because I recognise the love for what it is.”

Some names have been changed

• This article was amended on 26 April 2022. Lopez’s marriage to Cris Judd was her second, not her first, which was to Ojani Noa.