From Merriam-Websters definition.
"of, relating to, or characterized by a tendency to direct sexual
desire toward both sexes"
Referencing your original question about choosing to be gay. Dave, how do you know you love/enjoy sexual relations with women? Personally for me, the best answer I can come up with is "I just do". I think its the same for the majority of gays, its just the way they are wired.