I found your email address under a gay FAQ. I am quite young, and I know 90% that I am bisexual. I have tried and tried to tell my parents, but time and again, I get turned down, shut off or just plain tuned out. I am emphasising that word OUT. Well, I am a girl, or grrl rather. I find myself just wanting to be more discreet about this everyday. I have just recently came out to my friends, but they don't know what it means to be b/g/l. They think it is all about sex. But that is the way most teenage guys think of it.
You say you are young so I assume you are in high school or even younger and still living at home.
First of all, you seem to feel obliged to come out to your parents right away. I know this seems to fly in the face of what everyone else is saying, but maybe should wait until you feel absolutely ready before you tell them.
If you believe that they are going to be really upset, and most parents are at least at first, then you should be prepared with a safety network of friends who can provide you with emotional support. If you still live at home, things may get particularly uncomfortable for you. While I don't recommend that you lie to them, there is no harm in not coming out to them immediately.
Often young people who are financially dependent on their parents choose to wait 'til they are on their own before coming out to parents. While honesty is all very well, just remember that in our homophobic society that the cards are stacked against you!
Meanwhile you can prepare yourself for the day that you are ready to tell them. My first bit of advice is to read all you can. There are a number of books written by and for parents of lgb children and at least as many written specifically for you. The more knowledge you have the better prepared you will be for their reactions and the more informed you can appear when they ask you questions. There is so much ignorance around about homosexuality, and even more about bisexuality, that you can make yourself the resident expert.
Coming out as bisexual has its own problems; your parents will most likely point out to you that if you are able to fall in love with either gender why not make things easy on yourself and fall in love only with men. Also be aware that many parents hear bisexuality and immediately think of multiple partners.
As for people thinking it is all about sex, that, alas, is fairly common, even among parents. We hear it all the time at PFLAG meetings "I don't want to know what they do in bed." I point out to them that they don't think much about what their straight children are doing in bed or they'd probably be equally upset!
The bottom line is that you don't have to come out to anyone, least of all your parents, until you feel it is the right time.