There's a Girl in My Soup (1970)

TV personality Robert Danvers, an exceedingly vain rotter, seduces young women daily, never staying long with one. He meets his match in 19-year-old American Marion, who is available but refuses any romantic illusions. Her candor and cynicism put him off at first, but after he sees her breaking up with her rocker boyfriend, he's attracted to her and invites her on an idyllic fortnight in France. She slowly pokes holes in his artifice and he comes to care for her. When they return to Londonwith the press thinking they're married, they come to a crossroads: go back to their old lives, marry each other, or invent a new, open relationship. Is Robert up to it?