Betty Blue (1986)

Directed by Jean-Jacques Beineix, Betty Blue stars Béatrice Dalle and Jean-Hugues Anglade in a French romantic drama based on Philippe Djian’s novel. The film follows an intense relationship shaped by passion, instability, and emotional extremes, set against a contemporary French backdrop.

Från IMDB:
A lackadaisical handyman and aspiring novelist tries to support his younger girlfriend as she slowly succumbs to madness.