Bisexual just means you like both sexes. But there is a possibility of them liking one over another, like whether it's sex or relationship wise.
Maybe guys like guys for the sex and they like relationship better with girls, I've seen a lof of that lately.
But Bisexual is a stupid term, because once you find that person to be with, you aren't bisexual anymore, if you find a guy, your gay, if you find a girl, you straight. At least until you break apart and single again? =\
Then your bi again...it's a confusing term.