Thompson, 63, and Branagh, 61, met in 1987 when filming the series Fortunes of War. They were married two years later in 1989.
The couple divorced in 1995. It emerged that Branagh had been having an affair with Harry Potter star Helena Bonham Carter, 56, who he had starred opposite in his 1994 film Mary Shelley’s Frankenstein.
While shooting the film in 1995, the actor’s marriage to Branagh had ended. They had not yet made news of their split public.
The New Yorker writer states that Thompson was “humiliated, in part by her own stupidity” by the affair Branagh had with Carter.
“I was utterly, utterly blind to the fact that he had relationships with other women on set,” she said.
“What I learned was how easy it is to be blinded by your own desire to deceive yourself.”
Thompson went on to recall her mental wellbeing at the time, comparing herself to shattered dishes.
The Love, Actually star said: “I was half alive. Any sense of being a lovable or worthy person had gone completely.”
Thompson said that it had been her Sense and Sensibility co-star Greg Wise who “picked up the pieces and put them back together”.
Thompson and Wise have been together for 27 years. They married in 2003 and have two children together, Gaia and Tindyebwa Wise.
Branagh married art director Lindsay Brunnock in 2003.
Thompson said: “I’ve learned more from my second marriage just by being married. As my mother says, ‘The first twenty years are the hardest.’”
Thompson will next be seen as Miss Trunchbull in Matilda the Musical. Find The Independent’s review here.