My wife used to be bisexual. As a late developer, she wasn't attracted to boys in high school, but she liked the close friendships of girls, and that was able to segue into a bit of harmless experimentation. (She never had sex with a woman, though.) But she is now more attracted to men than to women -- and to a specific man (ahem) more than anyone else! She is also very shy, so it's not like she looks at specific girls or guys in public, and thinks, "Ya, I wish I could have some of that!" (We're very open about our stream of consciousness, our "raw thoughts in the moment", so I can say with confidence that she doesn't get crushes easily/impulsively.) She is incredibly, incredibly shy to people she doesn't already know.
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Christianity is different than Judaism only in people's minds -- not in the Bible.