On the other hand, who says he's gay? J. K. Rowling? Who cares what she thinks?
But it is possible that Ms. Rowling may be mistaken about her own character. She may have invented Hogwarts and all the wizards within it, she may have created the most influential fantasy books since J. R. R. Tolkien, and she may have woven her spell over thousands of pages and seven novels, but there seems to be no compelling reason within the books for her after-the-fact assertion. Of course it would not be inconsistent for Dumbledore to be gay, but the books’ accounts certainly don’t make it necessary. The question is distracting, which is why it never really emerges in the books themselves. Ms. Rowling may think of Dumbledore as gay, but there is no reason why anyone else should.Rothstein goes on to offer a couple of arguments to the effect that (a) it is not plausible that Dumbledore was gay and (b) gayness as an explanation of his weirdness would be considerably anticlimactic. More to the point, I think, given the allusion here to Tolkien: authors do not have the final say in what their stories mean or refer to. They offer one interpretation among many, and there is no reason to think that their own private vision of what their story is about is necessarily the best or even among the better visions. Tolkien, famously, did not think that there was any Christian allegory in The Lord of the Rings, and if we believed him half of the Ignatius Press catalog would disappear.
So I say, decide for yourself whether you want or do not want to believe that Dumbledore is gay, and then believe whatever you like, as neither hypothesis is supported or falsified by the available data. This is a classic case of underdetermination, and there is no wrong answer here.