It's important to know that a short boner when seeing another guy with a boner doesn't nessicerily mean you're gay, in fact, it is sometimes a natural reaction. If you're gay male, you will have these feelings for long periods of time, and again, girls will not turn you on. The same philosophy applies for gay females. Lesbians will have sexual feelings and desires for other girls and not have alot of sexual desires for guys. Bisexuality can be very complicated.
Bisexuals have feelings for people of their own sex as well as for people of the other sex.
The feelings may vary. Some bisexuals have more sexual feelings for one sex than for the other sex. No matter what kind of sexual feelings you have, it is important not to be scared off by them. Sex is part of every person whether they're gay, bi or straight. It's also important to remember that you were born the way you are but sexual feelings can always shift later in life.