I really want to come out but I'm scared to. The only person I feel comfortable coming out to right now is my best friend but I'm afraid that if I came out to her she would see it as a joke and wouldn't believe me just because a few weeks ago she came out to me and will think I'm just copying her. But the truth is she's the one who really made me think about my sexuality and finally admit to myself that I'm bisexual. I'm really conflicted as to what to do, should I go for it and come out or should I just wait?
Go through with it! I think she will understand. Even if she treats it as a joke and "doesn't believe you", she'll find out eventually she's wrong.
I agree that you should come out to your friend, since she might be more understanding because she has come out to you. She might even be able to help you or give you some advice, and if she does think your just copying her, then that says something and over time she probably will believe you
Your friend trusted you enough to come out. I think you can give the same trust back. I think you have an ally.