To complete the topic, which comes from a previous post, we should consider 2 definitions:
1) Biology: Sexual orientation refers to what or who induces a sexual excitation in you. What kind of people and what part of that people. The most important division is that of male-female, or the pair of opposites homosexual-heterosexual, which refers to you having the same genre or not, respectively. But be aware what I said before about sexual identity (biological and psychological).
2) Behaviour: Here we refer to how you behave, it means who you have sexual relations with and how does your body "function" (or not) in those situations. From this point of view, a person can be biologically homosexual, but "function" bi-sexually, for instance.It can be weirder too, for instance a person who functions well in any situation, but he/she needs to be watching a porn movie. Here the bi-sexuality is not the topic, but the conditioning of the movie (he/she would not function without the movie, in this example). Believe or not, it is very posible to happen such things as this... I´m a licenciate in psychology, so I know what I´m talking about.
Sexual orientation is fixed, so you must learn to live with it (your´s and other´s)