I believe that we are born with our sexual preferences embedded in us. Over time, experiences and our culture either amplify those preferences or suppress them within us. In other words, a man can grow up knowing that they are attracted to other men, yet society tells him that is not okay. He can either choose to be open and go against what society deems is an acceptable relationship or he can suppress those feelings and live denying he has them. A person can be curious but I believe they are curious to only validate what they believe they already know about themselves.
Personal Experience: I personally consider myself bisexual, however, I would not admit it openly (I would probably get stoned in the community I live in). I am attracted sexually to females but cannot connect in a relationship with them. I prefer to be "in a relationship" with a man but am not extremely attracted to them. To be honest, I can please myself but I want to have that mental connection with someone. In trying BDSM, I have been able to experience something higher than just physical gratification. I was the dominant and he was the submissive and our relationship was much more than sex. I told him what I wanted and he was happy to comply. He enjoyed pleasing me and I enjoyed not only getting what I wanted but ALSO pleasing him by letting him please me. It wasn't about whippings or treating him like a dog. There are so many levels that mass media doesn't show.

Note that I am probably not the best person to be commenting on this post considering I am in a dysfunctional relationship now. Just saying what I think though.