Ménage à trois
A ménage à trois (French: "household of three") is a domestic arrangement in which three people have romantic and/or sexual relations with one another, typically occupying the same household. A form of polyamory, contemporary arrangements are sometimes identified as a throuple, thruple, or triad.
History has a number of examples of ménages à trois relationships.
Speculation exists that, in 1547–48, Queen Catherine Parr, widow of Henry VIII, and her fourth husband Thomas Seymour were involved in a ménage with the future Queen Elizabeth. This is probably exaggerated, although episodes of sexually charged horseplay involving the three were well attested.
In his youth, thirteen years her junior, the French philosopher Jean-Jacques Rousseau was a protégé of the French noblewoman Françoise-Louise de Warens, who would become his first lover. He lived with her at her estate on and off since his teenage years, and in 1732, after he reached the age of 20, she initiated a sexual relationship with him while also being open about her sexual involvement with the steward of her house.
Sir William Hamilton (British ambassador to Naples), his wife Emma Hamilton, and her lover, the naval hero Admiral Horatio Lord Nelson, were in a ménage à trois from 1799 until Nelson's death in 1805.
At the age of 16, in 1813, the future author of Frankenstein, Mary Godwin, eloped with her to-be husband Percy Bysshe Shelley and engaged in a ménage with Claire Clairmont, future lover of Lord Byron, with whom the Shelleys would later have an extensive relationship.
The Belgian artist/illustrator Félicien Rops (1833-1898) maintained a remarkable ménage à trois with two sisters, Aurélie and Léontine Dulac, who ran a successful fashion house in Paris "Maison Dulac" They each bore a child with him (one died at an early age) and they lived together for over 25 years, until his death.   
In 1882 the Russian-born psychoanalyst and author Lou Andreas-Salomé invited the German philosophers Friedrich Nietzsche and Paul Rée to live with her, both of whom were in love with her. She kept her relationship with the two men celibate. Later she married a third man, Friedrich Carl Andreas, with whom she was also celibate.
In 1913, psychoanalyst Carl Jung began a relationship with a young patient, Toni Wolff, which lasted for some decades. Deirdre Bair, in her biography of Carl Jung, describes his wife Emma Jung as bearing up nobly as her husband insisted that Toni Wolff become part of their household, saying that Wolff was "his other wife".
As recounted by Arthur Koestler in The Invisible Writing, a conspicuous fixture of the intellectual life of 1930s Budapest was a threesome - a husband, his wife and the wife's lover - who were writers and literary critics and had the habit of every day spending many hours, the three of them together, at one of the Hungarian capital's well known cafes. As noted by Koestler, their relationship was so open and had lasted so many years that it was no longer the subject of gossip.
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