I think people did use to sometimes label themselves or others by behavior rather than orientation. I remember in one of Norma Klein's books a woman says of her ex-boyfriend "Also, he's homosexual, or was when he was younger." But in modern terms it's certainly bonkers to say that renewing your Bisexuality Card means you mustn't be monogamous, at least not for thirty-five years. (What's the necessary frequency of street-crossing, I wonder?)