Lady and the Tramp (1955)

After an upper-class princess (Lady) has a run-in with two devious cats ("We are Siamese if you please"), she and her working-class sweetheart (Tramp) embark on a memorable adventure around town that includes an accidental kiss over a plate of spaghetti. Despite a few relationship missteps, Tramp eventually disavows his streetwise ways, and the two reunite and have a family. It's really the template for the modern romantic comedy, before they felt compelled to always include an annoying best friend.