Well, the general message from both the straight and the gay communities is that you have to choose. They say you must pick one or the other, you can't like both at once, and if you can't pick, you're just pretending because you don't want to make a difficult decision (straight people say bi people are just "gay people who can't admit they're gay", while gay people say bi people are "straight people who want to pretend to be gay" or variations thereof). I have many gay friends who will remark, on a regular basis and in my hearing, that bisexuality doesn't actually exist at all. And in an environment like that, it's no wonder that you'd be confused and that you'd have a hard time choosing.
The problem is, they're wrong.
You don't have to like boys and girls equally, you don't have to be indifferent to the differences between them to be bisexual. You could have a 99% preference for men, but as long as you could also see yourself happily in love with a woman, I would consider you bisexual.
Actually, most bisexuals do have a preference. I'm pretty rare in that I don't. I'm called a 50/50. Most people lean towards one or the other.
The reason I'm so adamant about this is because I also had a hard time figuring out my sexuality. It took me about 3 years, actually. And that whole time, I kept looking around me and wondering, "Am I straight and just kidding myself that I find girls attractive because I think it's 'cool' to be gay? Or am I really gay and just kidding myself about finding men attractive because I don't want to go through the hardships of being gay? Am I one of those people who say that they fully support a gay lifestyle, but then hastily add that they themselves are not gay?" I honestly couldn't figure out which gender I liked better, which at one point convinced me that I wasn't sexually attracted to either (it's hard to know where the bar of sexual attraction is if you don't really have anything to compare it to). I considered the idea that I might be asexual before I considered the idea of bisexuality.
Basically, what that boils down to now is that every time someone tells me about a situation such as the one you're in, I tend to say, "Have you considered the possibility that you're bi?" I think if someone had asked me that, my struggle would have been a lot easier.