Vertigo
Alfred Hitchcock · 1958
Scottie falls in love with Madeleine, and he never falls in love with Judy. He rebuilds Madeleine in Judy's body by choosing the hair color, the clothing and the posture, until Judy becomes the woman he lost. The romance is about how impossible it is to love a real person when you're in love with a fantasy.
Where to see it: Scottie dressing Judy as Madeleine. The music scores the transformation like a love scene, and you only see how horrifying it is when you look back.