i lost a friend. she was being pretty mean to me though. this is how it all happened

one day in class she was telling me that she was mad because a girl was telling her to move in gym. i tried to talk to tell her in calmy why that happened and that the girl was only trying to help but she kept ignoring me and what i was saying. she just kept on arguing and eventually left angry or sad saying "well friends are suppost to stick up for each other." i didn't know if i should be angry or sorry. what did i do? i only tried to be a good friend be telling her what happened!and that's what i got? i pretended like nothing happened and just ignored her. i didn't talk to her for over a month because she never said anything to me either. she constantly stared at me trying to make me feel bad or something. and then my friend told me she was talking about me behind my back saying really mean things about me. and the worst part is she would sit next to me ( i have no idea why ) and i think she was talking about me then using some kind of nick name for me to make me look stupid to one of friends that are really mean. i felt so mad yet really sad. anyway, now ( over a month later ) she writes to me telling me why we're not speaking! she also mentions other silly things but i mean come on! oh, and what a coincidence, she writes to me right before a big trip we have. i don't think it is a coincidence though. i think she did that only to get a friend to talk to on the trip because none of friends are going. i emailed her back about how i felt about the situation. she acted like we were friends again and i didn't even say we were or for the matter that i forgave her.i finally stood up and told her through mail that i don't want to be friends after she truely proved to me that she didn't mean that she wanted to be friends. so yeahh. now i'm just really feeling down