If only there were clear lines! But, of course, there aren’t.
In one of my workshops, I have people fill out an anonymous one-page questionnaire. People are asked, among other things, to place themselves on a sexuality continuum from zero to six according to their overall score, and according to their behavior, fantasies, sexual and romantic attractions during different time periods—in the past month, before age 16, and overall. They are also asked what word or words they use to describe their sexual orientation. Once completed, the questionnaires are collected, shuffled, and redistributed, so that everyone in the room is now representing someone else in the room.
We then look at the data. It becomes clear that many people’s location on the scale varies depending on what period of time, and on whether you are referring to their behavior, their fantasies, etc.
Another consistent finding is that the terms “straight” or “heterosexual” are used by people standing not only on zero, but on zero, one, and two. The term “bisexual” is used by folks not only on three, but also on two and four—and sometimes also on one and five. The words “lesbian,” “gay,” and “homosexual” are used by folks not only on six, but also on four and five. There’s an overlap between categories, so someone standing on four, for instance, might identify as lesbian or gay, or as bisexual.
In no way am I saying that there are not people on the ends of the scale—there are indeed many. Rather, the categories of heterosexual, homosexual, and bisexual are broad, and encompass a wide range of experience.