We previously mentioned the Miller-Monroe-Montand love triangle. Here's a refresher: Marilyn Monroe met French actor/singer Yves Montand on the set of "Let's Make Love", effectively ending her marriage to Arthur Miller. Alas.
But there's another side to this triangle. (Which effectively makes it a love rectangle?) Montand was also married, and not just to anyone. His wife was acclaimed French actress Simone Signoret.
In fact, Signoret was the first ever French Oscar winner, for her performance in "Room at the Top". She then decided to put her acting on hold for the sake of her relationship to Montand... and this is how he chose to repay her.
And yet, because French people are French, Signoret and Montand stayed married until her death in 1985.
Oh, and Signoret was Jewish. How is that for a love rectangle? Let's go with love quadrilateral...