Sexual orientation, as you experience it, is a cultural construct.Wait a tic.
"You either are [homosexual] or you're not."
"I've had sex with heterosexual girls who wanted to be lesbian."
How could they "want to be"?!
You either are or you're not, right?
Except when you want to be...
The construct you understand is several decades out of date.
To truly understand human sexuality, you'd have to step outside of cultural constructs to look at human universals, and examine how cultural meaning systems influence how people conceptualize sexuality.
People inside a culture do not have to conform to the subjective meaning systems of that culture. A straight man could have sex with other men without ever identifying as a homosexual or bisexual. Sexual behavior and orientation and identity are not necessarily linked.