How do I tell my sister?

I know you guys are probably sick of these questions, but you all have helped so much(:

So I have been questioning my sexuality, and I know that I don’t need to put a label on myself, but I really think that I am bisexual. Though I am not 100%. But I have a sister who is a year and half older than I am, she is my bestfriend and we know EVERYTHING about eachother. We tell eachother everything, even if we don’t want too(:

So I want to bring up to her that I may be bisexual. I want her opinion and I want her to know! But I have no idea how to bring it up to her, and I have no idea what her reaction is going to be. I don’t want to make anything awkward or different for us. And I think that she is going to think that it’s weird. But I just want to bring up that I may be bisexual, nothing 100%

Should I tell her? Or should I just keep it a secret, even though I’m not sure if I can…

I’m really nervous and am clueless, so any advice?
Thanks!(: