Yes, JK Rowling did indicate that Dumbledore was gay. This isn't something that is mentioned in the book, but as an author or writer in general, you often write down traits about your character that you may never include in the piece that you're writing, but that will help you to better understand the character you're writing.
I'm not sure why, but I always found it quite obvious that Dumbledore was gay, so wasn't at all surprised when Rowling revealed it to be true.
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Aspie Quiz: AS - 141/200, NT - 77/200 (Very likely an Aspie)
AQ: 34/50 (Aspie range)
EQ: 32 / SQ: 68 (Extreme Systemizing / AS or HFA)
Diagnosed with AS and Anxiety Disorder - NOS on 03/21/2012