Dumbledore being gay isn't strictly necessary, but it does make the story make a lot more sense.
Most of what you said can be attributed just as easily to Dumbledore simply not being into sexual love. It's not like he talked of love and never explored it: he was adored by the wizarding world, had countless good friends and countless more acquaintances, and- except for the gay comments of Rowling- it could be inferred that he tried the whole "monogamous partnership" thing and decided it was best to focus on his career/purpose in life.
I understand we live in a laughably over-sexualized culture at the moment, but just because a character isn't married or a raging bachelor doesn't mean he plays for the other team.
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http://www.youtube.com/watch?v=SBpfwpOPXNc&NR=1&feature=fvwp
I watch Planet Chasers Starlight Excellent all day, every day.