Betty is the name of James’s former lover in Taylor Swift’s “august” love triangle.
The song belongs to a three-track narrative on Folklore involving Betty, James, and the unnamed narrator of “august.” In “august,” the narrator remembers a summer relationship with James. “Cardigan” presents Betty’s perspective, while “Betty” presents James’s perspective as he tries to address what happened.
James is already connected to Betty when the events of “august” take place. That makes the narrator’s romance with him temporary and uncertain, even though she experiences it as emotionally important. The songs do not present the story as a direct account of Swift’s personal life; they are fictional character studies.
A frequent misunderstanding is treating “Augustine” as the narrator’s official name. Swift has used Augustine or Augusta as informal ways to refer to the character, but the song itself does not give her a formal name. Betty, by contrast, is explicitly named in the connected songs.