Dumbledore’s story throughout the series was one of a kind man living with significant guilt over mistakes in his past and decisions he has had to make for an overall better future. From the first book we are shown that Albus would rather not look at or discuss himself or his past, but look ahead. His deflection of Harry’s question about what he see’s in The Mirror of Erised seen in the context of the series as a whole is obviously deeper than what was thought at the end of Philsopher’s Stone. Regardless of all, Dumbledore as a supporting, educational, and parental figure was still not the main character so his sexuality in the main story is not an issue.
As the creator of all of these characters, J.K. Rowling has every right to tell us at any time whatever backstory she has on them. Newly developed or in her mind from the start.
Personally, I’m hoping to hear how Seamus Finnegan and Dean Thomas are living happily together running a shop in Diagon Alley raising their kids.