Should I Stay Or Should I GO?

Sometimes it feels like the people you are closest to, are just around you because they want something from you. Lately I've been feeling that a lot. And it feels like it wont stop. Or the people wont stop acting that way, or it seems like everyone is mad at you, or gods out to get you. And when you don't know what you have done you cant do anything to fix it, and when you ask those people who are mad at you, they just say "nothing, I'm fine really, and I'm not mad at you." And its then that you know something IS wrong. That's how you can tell when one of your friends is mad at you. You feel kind of helpless and then when you cant talk to those people that you would usually talk to, to make you feel better, they aren't around. And when they want to suddenly become friends again, you'll be to happy to stop and think if they just want something. I have a friend like that, we have been friends for 5 years, and when she started coming to my school this year, there was this group of girls that we couldn't stand. And one of them was "dating" the guy she liked, she would call me and cry to me over the phone, when two of the people from our "group" left to join them, we made a pat saying we would never join them. One day my class had a field trip and when i came back i found out that she had been hanging around with them, its not my choice to choose who people are aloud to hang out with, but she should have just admitted it then that she liked them, maybe i wouldn't be feeling like this now if she had just done it. So when i asked her she said "well i needed to take the bus with someone and they were the only people around" and then this started happening more frequently and she would stop calling me and when i would call her she would just be like sorry i got busy or i was out, but then when she started hanging out with them at school i knew things would be different. Then she started coming up to me and being like "oh my god they are so annoying." and i was thinking OK, maybe we'll start hanging out again, but then she just kept hanging around with them. So then the other day she got in a fight with them and she came up to me and said "Allie, i know i haven't been acting like your friend lately and I'm sorry i hope you can forgive me and we can still be friends" and i didn't think much of it at the time, so i said sure, then the next day she starts hanging around with them again, and i was thinking "am i just her back up?" someone she can come to when she needs something. I will always be there for her no matter what but i just want her to do the same. There will always be that connection i had with her, but i want her to acknowledge my existence when were at school, and not just text me or call me when she wants to tell me a guy likes me (honestly that's the only time she calls me or texts me) and I'm sick of it, because if i am her friend, she would still be calling me, and like i said i don't give a shit who she hangs out with, but i would like to be acknowledged and still be aloud to talk to her without feeling out of place, i was there before them, and most likely i will be there after them, but i WONT be there, until she realizes that I'm still here, its not like Ive died or anything, I'm still here. Its a different case for everyone. This girl is only my friend because she wants something from me, and its not friendship, and its not money, she wants backup. And someday, when she needs me, i wont answer the phone.