Serious as Pleasure (1975)

In Serieux Comme le Plaisir, two men and a woman live quite happily together in a romantic liaison. The woman is probably wealthy anyway, so the trio doesn't worry much about money. One day they decide to take a trip in their beat-up car, managing the whole affair in their own special, insouciant manner. They are followed by a suspicious policeman who thinks there's something fishy about this group. As part of their play they tie the girl up, apparently leaving her behind, but she adamantly refuses to be rescued and heaps abuse on anyone who tries, including the hapless policeman. At some point she goes off with an Eastern monarch, leaving her lovers behind. She returns, and soon the trio is once again sniping at puzzled interlopers, playfully going about their business of confusing everyone. Later on in the film they are seen depositing their son at school where he is awaited by two young girls.