Jack Kerouac
© John Cohen/Getty ImagesOn the Road author Jack Kerouac listens to himself on the radio in 1959.
The former girlfriend of the leading novelist of the beat generation Jack Kerouac has revealed details of their affair and his descent into bizarre behaviour on finding fame, in a new book to be published more than 40 years after his death.

Joyce Johnson, an accomplished author, also dispels the myth that Kerouac's writing was effortlessly spontaneous. Where he claimed his novel On the Road was written in a blast of energy during three weeks in 1951 she recalls that he spent years revising his work and carefully crafted each paragraph.

Her book is just part of a revival of the cult that surrounded Kerouac which has this year prompted three feature films and a documentary, as well as books and an exhibition at the British Library.

Johnson, now 77, describes him as a "very odd person" who treated her dreadfully but was the love of her life. She delves more deeply into his background, his childhood and his rise to fame and chronicles the toll his celebrity status and his drinking took on their relationship.

She was 21 when she met Kerouac. "Jack was without a place to live and had no money. Since I was a young writer who had her own apartment, Allen [Ginsberg] set up a blind date." They were together for two years.

Kerouac became a sensation after On the Road, which blighted their relationship: "Women everywhere were offering themselves. He was a celebrity, which was very hard for him. In public situations, he had to drink."

Johnson's book, The Voice Is All: The Lonely Victory of Jack Kerouac, to be published this month, explores how the "spontaneous" writing of On the Road was actually "a much longer process ... each paragraph had to be a 'poem'."

She shows how Kerouac's French Canadian background both enriched his prose and gave him a unique outsider's vision of the US. She details his slow, often painful development as a writer, with early struggles to master English.

She said: "He spoke Joual, a Canadian dialect of French. Other biographies have not looked really deeply enough at the implications of Jack's Franco-American heritage, the fact that English was a second language ... There was always a process of translation going on, trying to find the English equivalent for the French inside his head ... Now looking at the text of On the Road, I can see French inflections all the way through it."

She recalls: "I thought I'd never met anyone who'd lived with more absolute freedom ... A need to keep moving, as if whenever he stayed anywhere too long, he exhausted the present by soaking it in too intensely."

Exhibits at the library will include the 120ft scroll on which he typed On the Road, according to his claims in 1951. After repeated rejection by publishers and years of despair, his story of a hedonistic road trip across North America was published in 1957, since when it has sold five million copies in the US alone.

Kerouac died an alcoholic recluse in 1969, aged 47, having tried in vain to interest Marlon Brando in a screen adaptation of On the Road. Francis Ford Coppola sensed the book's cinematic potential, but it has only now been made into a film, directed by Walter Salles, with Coppola as executive producer, to be released in Britain in October.

Rebecca Yeldham, one of its co-producers, said the story still connects with young people, particularly in times of adversity: "You read it through the lens of the moment that you're in, and through ... your own life experience. This book is still so timely and contemporary."

Kerouac's frenetic prose conveyed the energy of a postwar generation and the influence of jazz. It is said that he wrote with the freedom of a jazz musician, breaking the rules with grammatically irreverent sentences shaped by sound.

He is played in three semi-biographical films by Sam Riley in On the Road; by Jean-Marc Barr in Big Sur, an adaptation of the novel; and by Jack Huston in Kill Your Darlings, inspired by a true-life murder story told in And the Hippos Were Boiled in Their Tanks, by Kerouac and his friend William Burroughs, which was not published until 2008. Daniel Radcliffe plays fellow beat writer Allen Ginsberg.

Michael Polish, writer-director of Big Sur, said his film will show Kerouac's battle against alcohol and the pressure of being designated the voice of a generation. Asked why Kerouac had inspired so many films now, Polish suggested that, while traditional film-makers had been wary - "the books are hard to adapt as they don't allow themselves the typical three-act structure" - independent directors have shown how the rules can be broken.

There are also reports of a screen adaptation of The Dharma Bums, Kerouac's second bestselling novel, according to Paul Slovak, an editor at Viking, which is publishing a book on Kerouac by a former lover.

Isaac Gewirtz, curator of the New York Public Library, which has the world's largest collection of Kerouac papers, said his reputation as a serious writer had suffered: "His supporters see him as an inspired prophet; his detractors as a boorish man and artless ranter whose malevolent influence helped spawn the loathed counter-culture."

The scroll in the British Library exhibition was bought privately for £1.68m, a record price for a literary manuscript.