It makes sense that the Night Elf women are all at the very least bisexual. Ya see when they were introduced in Warcraft III the women were hunters and warriors while the men were druids who have been asleep for over 1000 years as part of some type of mediation ritual.
So I imagine that the women folk got antsy and that the goblin cucumber farmers just couldn't keep up with demand so one day a night elf lady said to her best friend, "hey, remember how my hunk used to kiss my women hood before I let him in my batcave? Well what if I did the same thing to you and you do the same thing to me?" And that's how lesbians were invented.