In her first US tour in seven years, Harry Potter author J.K. Rowling addressed an audience at Carnegie Hall and informed them that the character of Albus Dumbledore was gay.
Although the character's sexuality was never explicitly addressed in any of the books or movies, Rowling revealed that she had always envisioned his relationship with Gellert Grindelwald--who is discussed in the final book of the series--as a romantic one.
Maybe that's why he is always dressed so well.
Source: Reuters