What was Jean Le Rond d’Alembert’s relationship with Julie de Lespinasse?

The relationship between Jean Le Rond d’Alembert and Julie de Lespinasse was characterized by deep, unrequited love on the part of the mathematician. After d’Alembert suffered a serious illness in 1765, he moved into Lespinasse’s home, where he became the leading intellectual figure in her prominent Parisian salon.12

While they may have been intimate for a short period, d’Alembert’s profound romantic feelings for her were never returned. Lespinasse remained emotionally preoccupied with other men, most notably the comte de Guibert, a fact d’Alembert did not fully discover until after her death in 1776. Despite the lack of reciprocated romantic love, d’Alembert remained a steadfast friend and companion to her throughout their time living together. Following her passing, she left him the letters she had written to Guibert, which d’Alembert only then realized were intended for another man.12