Quatre nuits d'un rêveur (1971)

The 'dreamer' is Jacques, a young painter, who by chance runs into Marthe as she's contemplating suicide on the Pont-Neuf in Paris. They talk, and agree to see each other again the next night. Gradually, he discovers that her lover promised to meet her on the bridge that night, and he failed to turn up. Over the next couple of nights, Jacques falls in love with her - but on the fourth night her original lover returns...