How do I come out to my friends as bisexual if I’m afraid that they won’t wanna be my friends anymore?

Your friends know how valuable you are as a person, and they'll understand that your orientation can't change the person you are, the person they always loved. And if they turn their back on you, maybe their affection for you was more superficial than it seemed. Those who really care for you will support you no matter what! It could help you to start by coming out with the people you trust the most, those you are closer to and/or those who expressed open-minded views and will likely support you. It's all about openly explaining how you feel and how you realized who you are, making sure to tell them they can ask you questions about things they don't understand and discuss it openly.