It's natural and healthy to want to open up, and if you're close with your brother and you trust him - then he seems like the perfect person to open up to, especially if he has some bi friends.

People always say you should talk to parents or teachers about these kind of things, and I think talking to someone older and more experienced is actually a good idea, but a lot of time older people can be awkward and a bit weird. Maybe if you know a "cool" teacher or someone you really trust then fine, but I otherwise I would probably say your brother is the best bet.

Good luck and let me know if there is anything I can help with I have gone through this kind of situation myself and it wasn't easy. Especially with other girls in my class to be honest!