At a reading and Q&A session, author Rowling was asked by a young fan whether Albus Dumbledore, the powerful and positive grandfather figure who leads the Hogwarts School of Wizardry and Magic, ever finds "true love."
"Dumbledore is gay," the author responded to gasps and applause.I don't think Ms. Rowling intended to imply that being gay precludes finding true love. She went on to explain that the great wizard had had a tragic love affair earlier in life. I think that puts him into the "only one great love" category of fictional folk.
My take on elderly deus-ex-old-guy characters like Dumbledore is that they exist beyond the age of any romantic entanglement. And for the span of time covered by the Potter that seems to be the case.
Of course, any good writer will know the back-story of all of her characters. And given that a percentage of any group of humans is gay, it makes sense that there should be some gay folks in Harry Potter's world.