A Few Days with Me (1988) on Netflix

Martial's mother owns a chain of supermarkets. He had spent some years in a mental hospital because of pervasive indolence. Hoping that an active task may improve his condition, he is sent to inspect one of the supermarkets. The manager had taken a large loan of money belonging to the firm. When exposed he expects to lose his job. Instead friendship develops between him and Martial who remitted the debt. A sexual relation begins between Francine and Martial, without jealousy from her boyfriend Fernand. Suddenly Martial disappears. He was called to his mother's sickbed. Francine took a job as a waitress. It is not clear if she understood that the owner of the bar would force her to do sexual services for some customers. To save Francine Fernand kills the owner. The only witness is Martial who says 'Run! Do you want to spend ten years in prison!' If he takes the murder on him, he will just return to the luxury hospital he recently came from. Only Francine saw a glimpse of Fernand and understood what really happened. The double sacrifice radically changed her emotions: she came to feel for Fernand as for an older brother and they parted.