Ah I love reading these replies! I would say for myself that I am heteroflexible as I have in the past been attracted to women, though if heterosexuality and homosexuality are two opposite ends of a sexuality spectrum, I am closer to being hetero than I am to being in the middle. There is something particular about owning and playing with men that turns me on astronomically.
I learned that the ancient Greeks and Romans followed the standard paradigm of marrying and being in heterosexual couples, but would have socially acceptable same sex encounters. Sexuality was not conceptualized then, and wasn't really done so until relatively recently!