I disagree about women being ashamed to admit that they are bisexual. Most women can't wait to tell their lgbt friends that they are , or their boyfriend, because it is seen as somewhat fashionable to be a bisexual girl or a lesbian in today's society. I had this one girl in school constantly flirt with me because she knew I was into girls. She didn't want me an was not genuinely attracted to me, but because I was a girl and she could flirt with me, I was sort of a novelty to her. Plus, I was always good for when there was no male attention. So I was always the next best thing. She always got ignored, because it was perfectly transparent what she was doing.
Now, for men? They are not as comfortable saying that they are bisexual and that is understandable. Men set the standards in this society. Straight men do, anyway. I think that that is one of the reasons why lesbianism is not seen as wrong, and male homosexuality and bisexuality is. straight men like lesbians and bisexual girls, but condemn the men of that nature, and society follows that notion.