In the late stages of writing John le Carré’s biography, a doorstopper of 600-plus pages published in 2015 to largely appreciative reviews, Adam Sisman received an email from the writer’s wife, Jane. Attached was a 22-page memorandum of 196 corrections from the author, some of which queried source material that, as Sisman coolly notes with the mild glee of the vindicated, came from le Carré himself. The entire project – not an officially authorised biography but one undertaken with the knowledge and, to varying degrees, the cooperation of its subject – had been something of a push-me, pull-you affair.

Since the author of novels including the Smiley trilogy, The Night Manager and The Constant Gardener died in 2020 at the age of 89, there has been plenty for the aficionado to grapple with: a collection of his letters from 1945 until his final days, edited by his son Tim, who died in 2022, and the melancholy, rainswept Silverview, his 26th novel.

Now comes Sisman’s addendum to his previous book, one that concerns itself largely with the writer’s fondness for “a full and frank exchange of views” – his euphemism, borrowed from his conman father Ronnie, for sex (an illuminating aside in the book notes that le Carré tended to put this kind of “Belgravia cockney” into the mouths of his more dislikable characters).

Le Carré exchanged views with a lot of women, and several have their say in this book. Last year one of them, Sue Dawson, published her own account of their relationship, which began in 1982 when she worked on the audio version of Smiley’s People. (The Secret Heart was written under the semi-pseudonym Suleika Dawson, echoing Max Beerbohm’s 1911 satire Zuleika Dobson, about a woman so irresistible that she drove men to mass suicide, which is not quite the way it went for Sue.)

He called her his Recording Angel, and there are many champagne lunches, five-star hotels and clandestine trips to remote islands, accompanied by impassioned declarations of love, woeful descriptions of his domestic travails and demands for discretion interspersed with faintly obnoxious flauntings (he is pretend-horrified when they run into Frederick Forsyth in a supposedly out-of-the-way Chinese restaurant, although it doesn’t stop them going back to the Forsyths for a post-lunch brandy, of which there are also many).

Sue was but one: there was also a dalliance with a pal’s wife, an affair with an American reader that was almost entirely epistolary, an MI5 typist, a French woman who died in a road accident during an aid mission in Kosovo, an au pair and a journalist killed in an embassy bombing in Beirut.

Back in Cornwall, his second wife Jane kept the home fires burning, apparently tolerant of her husband’s infidelities as long as they were kept at arm’s length. It is worth emphasising that we do not have her side of the story and that she died not long after her husband; it is both of their deaths that, explains Sisman, have left him free to write about an aspect of le Carré’s life that he had deliberately left out of the biography. This was primarily to prevent his subject withdrawing access completely but also, one feels, out of a moral obligation to his wife.

It’s unsurprising, then, that Sisman – who is a delicate writer keen to acknowledge the ambiguity of the biographer’s role – is at pains to explore le Carré’s sexual restlessness in terms of his excruciatingly unhappy childhood and his comparative failure as a spy. Did he hanker after the career of a double agent so much that he imported it into his emotional life, whatever the cost to those around him?

He appeared to be a romantic partner almost entirely comprised, in the modern parlance, of red flags. But some of his more preposterous behaviour as a lover – the mawkish devotions, the extravagant gifts, the sudden cooling of affection – do indeed speak of someone monstrously unhappy; someone, perhaps, who never felt quite right in his own skin, and had to invent his way out of it.

• The Secret Life of John le Carré by Adam Sisman is published by Profile (£16.99). To support the Guardian and Observer order your copy from guardianbookshop.com. Delivery charges may apply.