In case you thought rocky celebrity unions (and public obsession with them) were a contemporary phenomenon, Stephen Galloway’s best-selling book about the marriage of Laurence Olivier and Vivien Leigh will tell you otherwise.

“They were lovers as famous as Burton and Taylor or Bogie and Bacall but their kind of love seemed closer to hate,” writes the former executive editor of The Hollywood Reporter in “Truly, Madly,” which arrived in the world only five days before the Oscars landed another high-profile couple on the connubial hot seat. “They appeared to have it all; and yet in their own minds they were blighted, doomed by a mental illness neither understood that transformed their relationship from the stuff of dreams into a living nightmare.”

Leigh suffered from bipolar disorder, then known as manic depression (it was diagnosed by the same psychoanalyst who, according to Gore Vidal, advised Tennessee Williams to give up both writing and sex so he could be “transformed into a good team player”). As our critic noted, Galloway is “perhaps the first author to interpolate this oft-told story with commentary from contemporary mental-health experts,” lending a new sensitivity to exhaustive analyses of the Olivier-Leigh alliance.

“People thought Vivien was just nuts and alcoholic,” Galloway said in a phone interview. “They had absolutely no sympathy for the fact that she was in the possession of a very serious illness that changed her behavior.”

What was it like to become a detective on the trail of someone else’s relationship for four-and-a-half years? “It was fascinating,” said Galloway, who immersed himself in Olivier’s archive at the British Library and Leigh’s at the Victoria and Albert Museum. “At the same time you ask yourself, morally, am I doing the right thing? Is it legitimate to be accessing not only their most intimate letters, but then publishing them?”

As for what he realized about love from examining troves of old correspondence and diaries — the kind of hard copy paper trail that may not be available to a future biographer of, say, Will Smith and Jada Pinkett Smith — Galloway was reflective. “What you learn is tragic,” he said. “How, even with the greatest, most all-consuming attraction, a little bit of sand in the oyster can become a dark pearl. How, if you’re not careful, little things can build and build until this boulder tips over and crushes the relationship. I don’t know how you prevent it. That’s a cautionary lesson.”

Elisabeth Egan is an editor at the Book Review and the author of “A Window Opens.”

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