Swift told fans in a live video that a trio of songs on the album portray a "teenage love triangle," but she didn't specify which three. The most popular theory is that the three songs in question are "August", "Betty," and "Cardigan," each told from a different perspective.
In this reading, "Betty" is from the perspective of James, who admits to having cheated on her but also is frustrated she's been listening to rumours started by Inez. "Cardigan" gives Betty's point of view and follows her feelings before, during, and after their breakup. And Inez gets to tell her story in "August," where she reveals her summer fling with James that was always doomed because he was still in love with Betty.