Dangerous Liaisons

“…when Sartre couldn’t get Olga to sleep with him, he seduced her sister…In 1945, Sartre went, alone, to the United States, where he met and began an affair with Dolores Vanetti, a Frenchwoman who...was married to an American doctor…In 1947, Beauvoir went, alone, to the United States, where she met and began an affair with Nelson Algren. … In 1952, when she was forty-four, Beauvoir began her affair with Lanzmann, who was twenty-seven. In 1953, Sartre began an affair with Lanzmann’s sister, Evelyne. She was twenty-three.”

That's Louis Menand, writing about the charming home life of Existentialism's First Family.