This is a question asked by a friend of mine named Wynsley Medel in her blog post "2. Bisexuality and Relationships." at wynsleymedel.blogspot.com. It is true that many are asking this same question. Since a person has a larger variety of whom to be attracted to, most of us would think that this same person will have greater chances of having an affair. However, the real confusion here is not about them having an affair. It's about them, existing. I am not saying that they should not have existed. But what I'm trying to say is that there have been gays and lesbians, why choose to be neither, or both (I apologize for having not known if bisexuality is neither gay nor lesbian or both).
I tried to search about the different reasons why a person would end up being bisexual. There is a letter, posted online, that i have read. It was entitled, "Can I trust a Bisexual Woman?" by Benjamin Caplan. It was a letter written for someone named Tetty by a lesbian named Cheryl, who had had two girlfriends, who both ended up having boyfriends. In Tetty's reply she mentioned:
"The Kinsey Reports, researched then written in 1948 and 1953 at a time when attitudes about sex and sexual orientation were much more closeted, showed that adults show an extremely high rate of sexual “reaction” to both the same and opposite sex. Dr. Kinsey and his colleagues determined that at least 50% of people had sexual feelings towards both genders. This information has not been refuted since that time.
I do believe that there are lesbian and gay people too afraid to confront homophobia and never manage that transition. Additionally, as it is argued, there is probably some truth that some people choose “heterosexual privilege,” who otherwise may be gay or lesbian. But the biggest thing I’ve learned both as a human being and as a therapist is that the world and it’s possibilities are huge. There is such a wide spectrum of interests, attitudes and beliefs. So much of life is not black or white, one clear way or the other. Diversity, so often talked about is real. Also, we human being are not static. We change and do so constantly. Likes, dislikes, needs, wishes and so much more change through the course of our lifetimes, sometimes again and again."
This statement shows that bisexuality is sort of genetic and a social influence, having change as a result. Since an unrefuted study "The Kinsey Reports" (Sexual Behavior in the Human Male and Sexual Behavior in the Human Female) by Dr. Alfred Kinsey, et al, says that we half-like boys and half-like girls, then we are subject to changing who we are attracted to.