The boy in Taylor Swift’s “august” is named James.
The song is part of Folklore’s fictional teenage love triangle. In “august,” an unnamed girl recalls a summer relationship with James, who ultimately leaves her and returns to Betty, the person he was already connected to emotionally.
James’s story continues across the companion songs “Cardigan” and “Betty.” “Cardigan” presents Betty’s perspective, while “Betty” gives James a direct narrative voice. Listening to all three tracks reveals overlapping events from different points of view rather than three unrelated romances.
The narrator of “august” is not named in the song’s Wikipedia summary, which is why “Augustine” should not be treated as the canonical answer to this question. The song’s named male character is James.