ANd why is this a big deal???

So apparently J.K. Rowling envisioned Albus Dumbledore as being gay.

Great. But really, so what?

A fictional character, who has been killed off, who has been pretty much asexual throughout the story was envisioned as gay by the character's creator. Does it affect teh story line at all?

Not as she wrote the books. I suppose it could have, as part of the back story around Grindelwald. But since it wasn't mentioned it makes no difference.

Why make a big deal about it?

Unfortunately some will. And some will look for "sinster overtones" in all of the interactions between Dumbledore and Harry.