@justateenagegirl oh my God, it must suck so much to be jealous of your best friend. You must be trying not to get jealous cause she's your best friend, but the tries fail every time. My advice for you would be that tell her about this. You say she's your best friend, and a best friend is someone with whom you can share anything and everything with, without any discomfort. And that includes your feelings, even when they are about her.
So my advice is that talk to her about it. Confess that you are jealous. I know it may seem pretty weird when I'm saying it, but trust me. Talking about it with her will make you feel a lot better and she would ultimately be the one who'll try to find a solution. Tell her that you can't help it but feel jealous. You don't like it when you feel like a useless sidekick when you're with her, how it upsets you that boys only notice her, and use you to get to her. Tell her everything.
And if, somehow, she gets mad at you for this, then she's being very unreasonable, and you should tell her so. Cause all of this isn't your fault, so there's no reason for her to be mad at you.
My advice for you can only become plausible if you and your best friend are AMAZINGLY CLOSE. That's it. If she doesn't act like a best friend in some ways -- like forgetting your birthday, socializing more with people than you, and whatnot, then don't try this. Instead, find new friends.
I hope my advice suits you well and you are able to solve your problem. Good luck!