Best Friend? So nice / then so mean!?

Allright! My best friend, lets call her pansy. So pansy is awesome, we hang out a lot, ride the bus together, on and on. But then there is another girl, we shall call her Mel. When Pansy is with mel she acts different and she is rude. She leaves me behind. I dont tag along but hmm here is an example. Pansy invited me over for a sleepover. I go packed and everything and we start having dun whn Mel comes over and says hey pansy im having a sleepover, wanna come, oh wait look who's here. I am to nice! I left and said go ahead b/c we had a sleepover the weekend before. Mel is only here every other weekend. Whould I stay friends with Pansy? Or is she using me when she is bored? >=-(