How do I confess to my friends that I’m bisexual?

I know what you're going through, and my advice would be to casually bring it up. Do you and your friends ever talk about celebrity crushes? If so, you could mention a famous person of your own gender to see how they react. Like Alex said, it's also easier to confess through text or an online chat- when you can't see anyone's face, it becomes less stressful.

I can tell you my experience, in case it helps. I told my best friend I was bi through a facebook chat about a year after I decided I liked girls. I'd been teasing her about a crush she had on an anime character, so I said "you can date him, I'll date his girlfriend ;) (btw, I'm bi, so I don't mind)".

Your friends should be supportive of you! So I wouldn't worry about what they're going to say. And as the other comments have said if they don't accept you for who you are, you're better off without them. My best friend came out to me a year after she realised she was bisexual, it's not a big deal. It made me feel bad that she felt like she couldn't talk to me about things without thinking "what if" They're your friends, they'll accept you and be supportive of you along the way. Don't feel afraid to open up to them. Hope all goes well for you :)