On the personal side, let me say that being bisexual just means that you recognize within yourself the ability to love or to be physically attracted to members of both genders. It means that you are able to appreciate both genders sexually. Once this part of yourself is recognized, there is often the desire to experience what sexuality is like with both genders. After this is experienced, many bisexual people find that the difference in those sexual experiences create a desire to continue partaking of that diversity. But people are not just their genders.
Most people also consider sexuality to be an extension of love.
That leads us to people who are polyamorous. Polyfolk find within themselves the capacity to love more than one person at a time. This can often be confusing as our society denies the reality of this possibility. How you feel about one person has nothing to do with how you feel about another. This is a given.