Just a thought

Bullies are just people who are super insecure so they pick at other people's flaws to make them feel better about themselves. You should never have to worry about how people are going to react, so long as YOU are okay with who you are.
Are you gonna maybe get a bad reaction or 2? It's possible. But most likely, you'll be accepted. (for the fact that you still like girls... horrible way to think of it, but it's sometimes how people's minds work. ( '_')
You're a larger kid for your age... is that muscle? Not that it matters. ^^;
Anywho... you say that people might be afraid of you? Why might that be? Are you a nice person, or do you tend to be kinda be a jerk? Either way, (I bet you already know this), but respect is earned through kindness and not fear. ( ^_^)b
I guess, in the end, it's based on how you treat others? If you accept them, then they will accept you. ^^ Otherwise... you're in for a rude awakening... ( ono)p

 

I say go for it! tell them that your bi.
if you start to get bullied tell a teacher or another adult, i did that when i used to get bullied at school, and your friends will support you on your coming out or they are not true friends. the most important thing is to stay positive, as long as you keep your head held high nothing hurt you. also (to me anyway) it is just one piece of information it's not like you are going to automatically start acting like a complete stranger to anyone, because you are the same person your friends became friends with you. remember it is not the end of the world. if you need any more help just ask!

 

Okey-doke. ^^ Then, in your case, I honestly think you'll be fine! ^^
Good luck, and stay strong bro! *hug*