“It was the moment she kissed me in the sun temple that I thought, ‘Oh, my God, now I can touch the sky!’” says Pradyumna Kumar Mahanandia, known as PK, remembering his wedding day in January 1976. PK was a street artist, from what was known as the “untouchable” caste, in New Delhi, drawing portraits of tourists, when he met a young Swedish traveller, Lotta von Schedvin, after she asked him to draw her in December 1975. Now, after more than 40 years of marriage and two children – they can still remember every tiny detail of their meeting.

“We knew we had been together before – that this was just a reunion,” says Lotta. “A marriage like this means you are married physically and spiritually. We know our bodies will be recycled in a few years, so we believe that we’re always united in oneness.”

PK, who is huddled in close to Lotta as we speak via Skype, holds up a fragment of palm leaf inscribed by an astrologer and given to his parents on the day he was born. “This has run like a thread throughout my life. It says that I would marry a foreign lady with white skin who was musical,” he tells me. “I knew it was Lotta as soon as I saw her.”

A few days after they met, the couple made the journey to PK’s home village in Orissa, in the east of India, to meet his family and get married. Although his mother had died, PK’s father gave them his full blessing. But their early married bliss was shortlived. Lotta needed to get back to Sweden to continue her studies, so she climbed back into her VW campervan with her companions and began the long trek overland through Asia and Europe.

For some youngsters, intoxicated by love, and with dreams soon to be replaced by the realities of life, this might have marked the end of the affair. Not so for PK and Lotta. Letters flew between the two, sometimes delivered by other travellers on the trail who had heard their story. Still sketching tourists in his usual spot in New Delhi – “I did Swedes for free,” he says, laughing – PK started planning the seemingly impossible, an overland journey of 7,000km to rejoin Lotta in Sweden.

“Flying was out of the question,” he says. Eventually, he realised a pushbike might offer him salvation and bought a ladies’ Raleigh because it was half the price of the men’s model. Then he set off with his passport, a spare pair of trousers, a sleeping bag and a windbreak – and $80 sewn into his clothes. The first night he slept, somewhat soggily, in a rice paddyfield. He continued travelling through Pakistan, Afghanistan, Iran and onwards.

Lotta, who had had the luxury of travelling in a vehicle and with friends, says the route was tough, but PK recalls it fondly. He says he became part of the “family” of the hippy trail. “We helped each other out. We looked after each other – I felt acceptance and love from people I met,” he says.

He talks of how he helped a German girl, after a car accident in Afghanistan left her badly injured and with no teeth; and of how a Belgian traveller kindly pointed out to him that Sweden was, in fact, a different country from Switzerland. “It was a bit of a blow to realise I had even further to go than I thought,” he admits ruefully.

His talent as an artist attracted attention along the way. He managed to get past the truculent border guards into Pakistan by drawing their portraits, and eased the difficulty of an out-of-date visa by sketching a government bigwig. He earned enough money to eat and travel – Lotta says being an artist was a kind of currency for him. “He could become very close to people quickly. When you draw them, they trust you – that surpasses language.”

PK thinks he helped people along the way, too. “In Herat, I met a man who saw me sketching. He was an artist, too, and invited me to meet his students. He was in love with one of them, and was fascinated that I was travelling so far to find my own love, when his forbidden love was sitting in his class. He told me he would be killed if he married her. I told him not to care about the system, to follow his heart.”

Subsequently, PK found out that the couple had travelled to Russia after the invasion of Afghanistan, where they had successful careers and a happy marriage. “I was very moved when I realised I may have given them some inspiration.”

PK ditched the old bike and bought a slightly less shonky one. He was getting there, slowly but surely, buoyed by friends he made and regular airmail letters from Lotta. Were there any doubts at all? “On the journey, I had doubts that I would die and wouldn’t be able to fulfil my meeting with Lotta,” he says. “But I knew in the next life I would find her. So, it wasn’t that I was doubting my love for her, more that I didn’t know whether I would make it alive,” he says. Lotta adds that she had no doubts. “It was just a matter of time that you would turn up,” she says. “His journey was a test for us being separated.”

The first photo of PK and Lotta together. Photograph: Courtesy PK and Lotta

PK’s journey was accelerated when Linnea – the German girl he had helped after her car accident – now safely back home in Germany, sent him a train ticket to Vienna, and again when a gallery owner in the city, impressed with both his story and talent as an artist, handed over the means to the final leg of his journey – tickets to Copenhagen and on to Gothenburg.

About 16 months after their parting as newlyweds, PK and Lotta found each other again, outside the town’s Salvation Army guesthouse for young men. It was a moment of intense emotion. PK, overcome with excitement and tiredness, started to cry. Lotta took him for a walk in the local park, where they sat among the flowers, drinking coffee.

“It was a great step for my parents to embrace our lives together,” says Lotta. “My mother had been initially cautious and my father was not a talkative man, but I had my willpower and strong belief that this would work.”

Soon, the whole family moved to a farm and lived in a more communal way. “We were more a joint family – a bit like in India. That’s quite rare in Sweden, so I guess we were a little bit odd in some ways,” she says.

They never seriously considered returning to India to live. They are sure PK’s budding political activism would have endangered them. “I escaped from India, really,” he says.

They set up a scholarship for children in PK’s village, and have since spent much of their time involved in various charitable projects in the area.

Their children, Emilie and Karl Siddhartha – known as Kid Sid – are now 31 and 29. “I love that they know that as soon as we met, we wanted to be with each other,” says Lotta. “They are very aware of our spiritual link, that we will never be separated. It’s an important message for everyone. We humans separate each other so much, but we’re all from the same source.”

The couple are convinced that the analogue era of the 70s helped build their relationship, through trepidation, heightened emotion and the anticipation of reunion. “I think those things have been lost now, in a digital age where you can so easily get together,” says Lotta. “There’s no chance to tune in, to use your sixth sense about someone now,” says PK. “Bumping along on my bike, my goal was always just to get to Lotta,” he adds.

And the secret of their long and happy marriage? “We’ve always said there is no secret,” says PK, all the time looking at Lotta, while her arm wraps around him. “I mean that literally – never have secrets. Talk to each other. Love each other. Celebrate your differences. And we find ginger tea and yoga in the morning help, too.”

• The Amazing Story of the Man Who Cycled From India to Europe for Love, by Per J Andersson, translated by Anna Holmwood, is published by Oneworld, £12.99. To order a copy for £11.04, go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders minimum p&p of £1.99.