The way that Dumbledore continued to ignore what was the right thing to do with regard to taking down Grindelwald indicates to me that he cared about Gellart on a lot deeper level than friendship.
Not to sound like a complete fruit, but I've gotta chalk this up to people underestimating the power of friendship. A real friend is just as strong a connection, if not more so, than a romantic lover. Sometimes you can really tell apart a strong friendship from passionate love is if the person starts acting crazy, but even then, Dumbledore never really seemed to lose his cool.
--
http://www.youtube.com/watch?v=SBpfwpOPXNc&NR=1&feature=fvwp
I watch Planet Chasers Starlight Excellent all day, every day.