[Retroman]

The story is anything and everything that comes from J.K Rowlings mind.
If she wrote the entire story and thought of Dumbledore as a gay character, it is her character and is automatically gay for everyone whether we like it or not.

She just thought it best to leave any gay storylines out of the books, which is a wise choice when dealing with children as fans. It'd be strange to write anything else in to confirm his sexuality, eg. "Hey Harry, im gay" just wouldn't work.

Apparently it shows the relationship and thoughts behind Dumbledore's liking for Gellert Grindelwald, so it does play a small part in the story and a major part in Dumbledore's character.