A question about a french movie I'm looking for

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for someone who is looking it out for a friend who saw it long time ago and saying it changed her life. so if you can please tell me the name of the movie by its description- There's a woman who goes to the supermarket and an old man picked on her, commenting on everything she is buying (not good, not healthy, etc') she is trying to get rid of him and eventually finds herself taking him home. the old man revealed as an angel who saves her from her frustrating life and eventually becomes her lover, telling her that when he will die, he want her to be in a little black dress near his grave. when he dies a lot of women coming to his grave, all in a little black dress and the heroine actually realizes what he did his all life - entering into homes of women to save her lives and disappear.