My friend told my crush I liked him, and I don't know why she's mad at me?

It was my first school dance. My friend (who's also a girl, we'll call her S) told my crush (we call him Spaghetti) that I liked him. Even though she promised she wouldn't. I got really mad but I didn't get the chance to talk to her about it. But she kept trash talking another one of my close friends. Then S got mad at me for no reason, I don't know what I did wrong?