Ed Sheeran is basically the male Taylor Swift, in that his songs are heavily biographical and fans love to pick apart the lyrics to figure out which ex or celebrity feud he's singing about.
It wasn't a difficult task with Sheeran's song "Don't," particularly with comments that Ed made in a recent interview with Howard Stern that basically confirmed the most popular fan theory.
"Don't" is about an ex of Ed's cheating on him with one of his close friends. Sheeran briefly dated Ellie Goulding last year and after they broke up, she had a fling with One Direction singer Niall Horan.
Ed is (or was) friends with the guys from 1D, so many fans assumed that "Don't" is about the Ed-Ellie-Niall situation. And then Ed basically confirmed it yesterday: