There's a lot that go into answering the questions you've asked, because they're incredibly broad.
Firstly, you have to look at the separate issues of bisexuality and a romantic attraction, as indicated by the first response.
Who you are romantically attracted to and who you are sexually attracted to tend to line up for the majority of people. However there are many individuals who feel that their two attractions do not focus on a common type of person.
Those who identify as bisexual are, in most cases, both sexually and romantically attracted to members of either sex. Effectively, they ignore the issue of gender and are attracted to specific attributes about people.
Within this group there are subsets, people who find a neutral attraction to either men or women (that is to say that the attraction is equal for both sides, based solely on individual traits) and those who, despite having attractions to the same or opposite sex, feel those attractions more strongly for members of a particular sex by default. That is to say a person can be bi, but with a preference for men or women.
Whether or not a person 'fakes' having a non biased (bi) sexuality or romantic attraction depends wholly on their situation. A person may falsify these feelings to support these feelings in a partner, or for other personal motivational reasons. From what I know though, these cases are not overwhelmingly common, though I'm sure they exist to some degree.
As for it being an 'acquired taste' in effectively all cases, I think that bisexuality is a trait of a persons birth, in the same confines as homosexuality and heterosexuality. I don't see reason to accept the positions on either side, or directly on the fence, as being anything other than the natural result of a persons brain structure.
To clarify for the final question, I cannot answer. I am gay, not bi.