Bi problems!?

Hi. I'm 13 and I'm bi. Nobody knows apart from my gay best friend. Recently I met a girl who is in the year above me in a show that I was in. She was really nice to me and we were gossiping for hours and had so much fun. She is also bisexual btw (she doesnt know i am tho... i dont think so anyways) and I think I like her. But... there is just one problem... SHE HAS A BOYFRIEND!? I don't know what to do. Like should i tell her? Or what???