Sexuality seems a petty matter  

More on Dumbledore from Edward Rothstein:

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.