“august” was the first song Taylor Swift wrote in the Folklore love-triangle group.
The three connected songs are “august,” “cardigan,” and “betty.” Together they explore a relationship involving James, Betty, and the unnamed female narrator of “august,” with each song presenting a different viewpoint or stage of the story.
Swift wrote “august” first, then developed the broader narrative around the other characters and perspectives. The song is told from the viewpoint of the girl who has a summer romance with James while he is already connected to Betty. The character was not given a definitive name in the lyrics; Swift said she privately thought of her as Augusta or Augustine.
The group is sometimes called a teenage love triangle, but “illicit affairs” is not one of its three songs. It is another Folklore track with a separate narrative, making it a plausible but incorrect answer to this question.