The Beauvoir/Sartre/Kosakiewicz Love Polygon
Jean-Paul Sartre and Simone de Beauvoir were really something else, even for philosophers. Sartre was an esteemed novelist, playwright, and critic, while de Beauvoir helped lay the foundation for the modern women's movement. Their romance was naturally ahead of its time; they even had an open relationship before it was cool.
Liu Dong'ao/Wikimedia CommonsAnd there's no "cool" like "Existentialist cool."
In most cases, it's assumed that the man is the one who initiates such an arrangement, while the woman merely endures it, but de Beauvoir was basically a French intellectual Hugh Hefner. Not only did she tally a long list of playmates, but she was also an honest-to-goodness sugar momma. One of her babies was Olga Kosakiewicz, the daughter of a dispossessed Russian emigre who studied under (and on top of and beside) her when she was teaching in Rouen. Promising to take care of her and even pay for her education, de Beauvoir moved Kosakiewicz into the Hotel du Petit Mouton, where she was also living. Hef could have actually learned something from de Beauvior, who cared about her bunnies' minds as well as their bodies.
On the other hand, she seems a lot less honest than Hef. When de Beauvoir finally had enough of Kosakiewicz, she introduced her to Sartre, who fell head over heels and tried to seduce Kosakiewicz for two whole years. But Olga wasn't into it, so she took a pass and found that there was in fact an exit. Right when Sartre had finally given up, however, Olga's younger and more receptive sister came to Paris. This seems like a fairly complicated configuration already, but then de Beauvior became bored with it all and decided to seduce Olga's new boyfriend, who later became Olga's husband, even though he continued his affair with de Beauvoir well into their marriage.
De Beauvoir mined the whole thing for material for her 1943 novel She Came To Stay, in which she combined Olga and her sister into one character who has lots of threesomes with a philosopher couple and then gets murdered. The book was dedicated to Olga, who presumably began sleeping with a mess of weapons under her pillow.
Frida Kahlo Slept With Her Husband's Hero, Leon Trotsky
Like Sartre and de Beauvoir, Frida Kahlo and Diego Rivera were a pair of artists whose sexual appetites couldn't be satisfied by only each other. But unlike the philosophers, they had no enlightened understanding. On at least one occasion, Rivera pulled a gun on a man he found in his wife's bed -- which was rich, considering he was probably on his way back from boning one of his own mistresses. Things came to a head when Rivera became sick and acted out on his resentment over his dependence on his wife's care by sleeping with her sister. Kahlo was devastated. Shortly thereafter, she slept with Leon Trotsky.
Carl Van Vechten/Library of CongressMaking us think that the line between being a groundbreaking artist and a Jerry Springer guest is thin at best.