Bisexual erasure or bisexual invisibility is the tendency to ignore, remove, falsify, or reexplain evidence of bisexuality in history, academia, news media and other primary sources.
Those of us who are bi, pansexual, queer or whatever you want to call it, know this all too well. If I am in relationship with a man, I am straight. If I am in a relationship with a woman, I am gay. If I'm in a relationship with someone who doesn't identify strongly with either gender, then no one knows what I am. I will either be straight or gay based on that person's perceived gender. And if I'm in a relationship with different people who fit all over the gender spectrum? Maybe then I finally get to be viewed as "legitimately" bi, pan or queer sexual. But usually not- since I am personally in a heterosexual marriage, I am still often thought of as straight.
One thing bisexual people hate being told is either that they must choose one gender or another, or that they will never be able to have a committed, long-term or monogamous relationship if they don't choose. Most bisexual people seem to hate the assertion that they can't be monogamous if they find more than one gender attractive. Personally, I hate the assertion that there's anything wrong with being non-monogamous. Either way you look at it, it is clear that our societal ideals and expectations for monogamous relationships play a heavy role in bi erasure and invisibility.
Whether or not a bisexual person chooses to be in a monogamous relationship, we need to stop defining an individual's sexuality based on the perceived gender of the partner they choose. The series Orange Is The New Black addresses this issue a lot. After Piper's fiance Larry learns that she has been cheating on him in prison with her ex-girlfriend, he asks Piper's brother Cal:
"Is she gay now?" (this is after Piper has already given him a lecture about the Kinsey scale and has told him she is bisexual earlier in the series).
Cal responds "“I’m going to go ahead and guess that one of the issues here is your need to say that a person is exactly anything.” Which is a fine and good answer, but doesn't totally get to the crux of the issue. The issue is Larry seeing Piper's sexuality as either being defined by her relationship with him or her relationship with Alex. Piper doesn't get to have any say in what her sexuality is, only her actions matter. She can only be gay or straight, and if she leaves Larry for Alex that means she's gay now.
Even within monogamous relationships everyone should have two sexual relationships. There is the sexual relationship they share with their monogamous partner, the relationship that is obvious to society and socially accepted. And then there is the sexual relationship a person has with themselves. Since the former involves another person, that relationship can be defined as straight or gay or whatever the two people involved want to identify it as. The latter, the sexual relationship one has with oneself, and all the fantasies and genders and anthropomorphic animals (if that's your bag) that exist within that relationship- those all belong to the individual. And the individual should get to decide how to identify. Alone. It's theit identity.
I have long said that I think the great downfall of monogamy is not the idea of only having one sexual partner; it's the ownership and possession that person gets to have over your sexuality that really gets to me. Not every person in every monogamous relationship always takes advantage of this implicit ownership, but it doesn't matter. Society views a monogamous couple as a solid sexual unit, defined by the sex they have together. There is no room for sexuality outside of that unit, even the sexual relationship you have with yourself.
It's maddening and it's sick.
I don't believe bisexual erasure will stop happening until people can stop seeing someone as being defined by who they choose to have sex with. You don't need to be non-monogamous to be bisexual (though it does help in my particular case), but you do need to be able to differentiate your sexual identity from your monogamous relationship. Possession has no place in personal identity and it's time we start allowing for individualism in our sexual identities.