It's not just the stuff of a Diana Ross ballad, but a real - if ephemeral - quality that some lucky couples manage to grow and nurture over a period of decades.
With 42% of UK marriages ending in divorce, we look at six happy duos who've bucked the trend to keep the spark of romance alive for fifty years or more.
From friendship to fidelity and an ability to weather the storm, they share their moving secrets of a love that time can't erode.
'He keeps on loving me and looking after me'
The couple: Margaret and John Beauvoisin
Married since: 1948
Their secret: "We have remained faithful and love our family"
Margaret and John got married on December 27 in 1948.
As they celebrated their diamond wedding anniversary a few years ago, they revealed that they had renewed their vows every year since 1950. Each time, they've taken their rings off to be blessed and put them back on again.
"It reinforces our promise to love and care for one another," said Margaret.
The pair met at a dance in Southsea.
"It was by accident really," Margaret recalled. "He was sitting in my chair and I went to sit next to him. Then he got up and I thought he was asking me to dance. He hadn't really intended to ask me it turns out, but we spent the rest of the night dancing and he saw me home."
After tying the knot, the couple went on to have 11 children together, leading to 23 grandchildren and 13 great-grandchildren.
Most of this enormous clan were on-hand to watch as these two lovebirds swapped vows for their diamond anniversary in 2009.
"He loves me and looks after me. We have remained faithful and love our family," said Margaret. "Unlike my mother I'm a terrible housewife really and not very good at keeping the house clean. But John puts up with that and keeps on loving me and looking after me."
John agreed, joking, "I still love her somehow."
'We are more in love now than ever. We keep each other going'
The couple: Lionel and Ellen Buxton
Married since: 1938
Their secret: "We have been good friends as well as husband and wife"
Lionel and Ellen counted as one of Britain's oldest married couples when they celebrated 75 years together in 2012.
Ellen, aged 100 at the time of the landmark anniversary, said: "We have never been apart really and have never wanted anyone else. We have been married happily because we have been good friends as well as husband and wife.
"We have always made sure we have had nice evenings out together. Whether it is going for a romantic meal or out to play bingo."
The inseparable duo from Dover, Kent, met in March 1930 and married six years later.
They did not spend a night apart since and shared a passion for darts, snooker and football (as Charlton Athletic fans).
Lionel, at 99 years old, called himself Ellen's "toyboy".
"She was lovely," he said, of the moment he met his future wife. "I always looked forward to when she needed help from me. We got on so well, went on a few dates together and became a couple. We ended up getting married. We would have done it sooner but could not afford it."
The couple went onto have a daughter, and four grandchildren.
They fought a number of battles together, including Ellen's diagnosis of bowel cancer at the age of 90.
"We are more in love now than ever. We keep each other going," Ellen said.
'It just hit us immediately - it takes a lot of love and work'
The couple: Alice "Nonie" Dubes and Vivian Boyac
Been together since: 1942
Their secret: "It takes a lot of love and work"
Alice and Vivian had been together 72 years when legal changes meant they could finally get married in a church wedding in Iowa last year.
Both in their nineties, the women wore warm-hued pastels and sat in their mobility scooters as they held hands during the moving ceremony, in front of close friends and family members at Davenport's First Christian Church.
"This is a celebration of something that should have happened a very long time ago," the Reverend told them.
Friend Jerry Yeast agreed, telling a newspaper, "I’ve known these two women all my life, and I can tell you, they are special. This is a very special day for all of us."
Vivian and Alice met in their hometown of Yale, Iowa, in 1942.
"It just hit us immediately – if you can understand that," said Alice. "Kind of like a regular marriage, the boy-and-girl meet … well, that was just the way we were."
Their wedding marked the first time they celebrated their relationship in public, after years of living and travelling the world together.
"I think a lot of people knew, but didn’t ever say anything – and we didn’t tell them," said Alice. "If they wanted to know about us, that’s their problem.
"We’ve been fine all along the way," she added. "I suppose we’ve had our ins and outs, but that’s how it goes with any relationship. We've had a good time."
Vivian added that "it takes a lot of love and work to keep a relationship going for 72 years".
Rev. Linda Hunsaker, the minister who held their marriage ceremony, has been in the business for 20 years.
"I’ve done a lot of weddings with some young people, and unfortunately I don’t think all those have lasted – and these two [Vivian and Alice] are the ones that haven’t been able to have their relationship? They are the model people that we want to be able to lift up," she said.
"The best part of it is all the love we’ve received, in response from all the people, noted Vivian. "It’s all been good."
'I tell her I love her ten times a day'
The couple: Sir John and Lady Mary Mills
Married since: 1941
Their secret: "We have kept it romantic. We have sent flowers, messages and never forgotten dates"
It was a special day indeed when the late Sir John and Lady Mills renewed their vows on their diamond wedding anniversary in 2001.
The first time around, in 1941, it was a rather more rushed affair for the Oscar-winning actor and his writer wife.
As a Royal Engineer, Mills was allowed just 36 hours off for the ceremony at Marylebone Register Office in London, before rejoining his unit.
"That wasn't my fault, it was Hitler's, the actor recalled in 2001. "I've been meaning to put it right for a long time."
Sixty years later and three children later, the duo once again exchanged (now old) golden wedding bands in front of a crowd of admiring friends and family at St Mary the Virgin church, near their home village of Denham.
At 92, Sir John was nearly blind at the time and his wife was suffering from Alzheimer's. But as the Mail reports, "she could still beam at her husband and clutch his hand as he spoke on behalf of them both in a clear, strong voice, and showered her with kisses".
"When I first came to Denham 12 years ago it was very evident that Mary was John's very special diamond," the rector said. "Now times have changed a little bit. We have talked about 'in sickness and in health' and now it is very definitely John who is Mary's great diamond. They have changed roles."
Explaining the secret to their marriage, John said: "When we married we decided it was a job and we have kept it romantic. We have sent flowers, messages and never forgotten dates."
In an earlier interview, Lady Mary talked about the importance of being in close proximity to one another, despite their hectic schedules."It was no good my being in Birmingham while John was in the West End," she said. "I believe that if you want to keep a marriage together you have to be together. There's always some little girl who finds a husband is misunderstood."
'We have got good humour, that's the key'
The couple: Cyril and Evelyn Sergeant
Married since: 1952
Their secret: "We are always joking and that makes the difference"
Cyril and Evelyn Sergeant, from Orpington in Kent, got wed on February 23 1952, the same month that Elizabeth II became queen.
This meant that the year of their diamond wedding anniversary coincided with the Queen's diamond Jubilee in 2012 - a happy coincidence that meant the couple got to meet the monarch at a special tea party.
The duo said that meeting Her Majesty made their diamond anniversary even more special.
In fact, Evelyn still remembers travelling to London to attend the Coronation as a newlywed.
"I remember it was pouring with rain and I had a red coat on. When I got home the rain had left red marks on my clothes," she said.
As to the secret behind their 60 years of marriage, she said, "We have got good humour, that's the key. We are always joking and that makes the difference."
'We just chose the right person the first time'
The couples: Jean and Peter Baxter, Pat and Ray Basson, Maureen and Ted Burst, Ann and Ron Valentine (all four women are sisters)
Married since: between 1951 and 1959
Their secret: "We stuck together through thick and thin. We had ups and downs, of course, but we dealt with them as adults"
The McAleney sisters - Jean, Pat, Maureen and Ann - celebrated a fairly remarkable anniversary in 2009, as it transpired that all four of them had endured happy, successful marriages of 50 years or more, and all within the same area of West Sussex where they grew up together.
Youngest sister, 69-year-old Ann, was the last of the four to mark her golden wedding anniversary to husband Ron, and the sisters used the milestone occasion to mark the 214 years of marriage they'd clocked up between them.
In true style, they celebrated with a garden party attended by their collective hoard of ten children, 22 grandchildren and two great-grandchildren.
The sisters attributed their long marriages to sticking at it and following the example set by their parents, who also stayed together.
"It's just the way we were brought up," said Ann. "We stuck together through thick and thin. We had ups and downs, of course, but we dealt with them as adults."
"The fact that we are all still together is that our parents stayed together and we were brought up to be a family so we have followed suit," said Maureen. "I just think there's nothing better. It's a good stable background if you are going to have children. We have been very lucky with our husbands and lucky they are still with us and get on well together."
"We just chose the right person the first time. This isn't going to happen in the future," said Jean. "People don't have stickability - at the first signs of a problem they just give up. If you have a problem you must work through it."
"Every marriage has hiccups but you should not part just because of that," added Pat. "We believed what we said in our wedding vows - for better and for worse - and we stuck by it."