Why should I care whats the point?

Ok so my supposed best friend, has been treating me like nothing. We just started seventh grade two days ago, and when ever her best friend comes around, she gets really excited and gives her like really huge waves or hugs and hellos. When I get to her she doesn’t even say hello usually and I don’t understand why, we had just had a two day sleep over and it ended well but now she just practically ignores me and I told her best friend about it, and she doesn’t understand either. What should I do she isn’t treating me like a friend, and I don’t even understand why I should care about our friendship anymore if I get nothing in return when I give a lot.