friends really your friends?, a problem =\ Options

[lovescream]

uhhh.. i have a friend who calls her my best friend.
we used to be as close as sisters can get.
but then one day she started to avoid me and hang out with some of the people we talk about. cierra broke her leg and my best friend is hanging out with her like she's her best friend and really hasn't talked to me on the phone/online since.

then i started hanging out with another friend and then the day i got detention and missed recess [elementry school me is in] my best friend started stealing my friend i was hanging out.
and they leave me out
so now i feel like i have no friends, no life, no nothing.

and just now i was talking to a male friend [i have more male friends than girl friends] and she all of a sudden wanted to talk to him and she used to hate him... now she's all over him like a dog. i haet the fact that she's taking my friends when she has friends of her own i practilly cant talk to.

i'm one of those people who like stuff to myself.. i grew up as an only child so i'm very used to that... so what should i do?
it seems like my life is falling apart. my best friend just talked to me today only because she needed help on the project and saying that oh i'm bored.
it's like i'm her replacement friend when she has no one to talk to.
i hate it.