Doesn't the word "spectrum" imply a linearity? Kinsey gave us a good start, but sexuality isn't this scale from homo- to heterosexual. It's better understood as a behavior, in fact. The acts of a person are homo- or heterosexual. We've only in the last 200 years started using sexual behavior as a marker for identity. If I identify as gay but have been attracted to a woman before, does that make me gay or bisexual? I identify as gay, so doesn't that make me gay, my past attraction to a woman notwithstanding? Sexuality is more like the way we understand gender nowadays: performative. It's only been recently in history that we've thought it as something concrete. It can change and it usually does throughout a person's lifetime. So it's best to take the actual labels with a grain of salt. What is gay? What is straight? What is a man or a woman? These are things that are culturally defined, and they don't usually reflect what's actually going on in the brain, which is much, much more nuanced and dependent on the situation.