Im soo sad. I think I'm losing my best friend..?

So we have been bff's since 2nd grade (7th now) but i feel like im losing her. There's this girl, who we played bball with. And she became really close with my bff. She always tries to make me jealous, and I'll admit it's starting to work. Like I'll be talking to my bff and she'll just come up and pull her away (literally!) But we're in different areas, so we really dont see her that much. But my best guy friend's dad is a teacher in eighth grade and everyone wants to get his homeroom. So we (me and my bff) walked down there after school so we could sign this paper to make sure we get in there. SO i turned around and that girl was right behind us. She runs up right between us and pulls her away. So we go in there to sign the paper and she comes in then my bff goes "hey if ur gonna get his hr u better sign this!" and so she signed it. So she is in my cl now. :P And besides that, today she (the girl) got to pick someone to help her with a soccer team thing. So they were gone alllll day. And I was sort of aggravated my bff and she comes in like" kelsey.. whats wrong???" and im like "nothing. Im just tired." Now I know i sound like a pathetic loser, but have any of u ever been in this situation? I really dont want to lose her!! What should I do!? And sorry this is so long.. THANKS.