Yeah, there isn't enough evidence. We've seen Sulu be courtly toward women but not which way his fancy truly goes.
I thought he did a fine job playing a human being. So we didn't know which way he swung, but that's okay! Zach Quinto didn't come out in "LOOK AT ME!" fashion, and you wouldn't know unless someone told you he was gay, right?
Very true.
Hopefully, once GT sees the reception and acceptance for Sulu being gay, he'll change his tune.
To quote a recent news article on this very revelation, sometimes art imitates life.