In the three French novels, the central characters all experience love as a fall. That is, love causes the characters in the respective works to lose their position. It makes them vulnerable, precarious, and in a sense, results in them falling apart.
In Jean-Jacques Rousseau’s novel Julie; or the New Heloise, the fall is immediate. In Saint-Preux’s first letter to Julie, he pleads with her to dismiss him from her life. He has fallen in love with her, and this love causes him considerable torment. By casting him aside, Julie would be doing Saint-Preux a favor, because such a banishment would supposedly halt his fall.
In the end, neither Julie nor Saint-Preux find a successful way to extinguish their mutual love. Saint-Preux sails around the globe. Julie gets married and starts a family. Yet Rousseau makes it clear that they still love one another, which suggests that once someone falls in love, the fall can't be easily controlled or stopped.
In Manon Lescaut, Des Grieux can’t seem to control his love for the eponymous character. She takes his money and cheats on him; only her death can possibly stop his fall.
In Dangerous Liaisons, one could argue that the absence of love causes the fall of Valmont and Merteuil. They view love as a means of manipulation, which destabilizes the lives of nearly everyone they come into contact with. Conversely, one could argue that Valmont’s true love for Tourvel reveals his vulnerability, which leads to his fall.