What Should I Do help me (friend probs)?

I think I'm a quite forgiving person but I'm just fed up of having arguments everyday I just want to get on with my life ; have a laugh,get good grades,make friends and more.Theres this girl and she's bullied two people but I thought she got a bit nicer but I guess not because everyday someone in a group as an argument with her it's all laughs, true friends and support with out her.Anyway today we had a break time without her (she went off but FINE WITH US) and we had the funniest time ever with our to friends that are boys (dw just friends lol) and i've been hanging round with this girl she don't like and she says oh shes taking u away when i really like this girl cos she is nice and a gd friend and btw she's the kind of friend that does things to someone and they dont like it but nofihappenses but when it happens 2 her its a MASSIVE crisis and she also asked out my bf as soon as i dumped him.ANYWAY, basicly what should i do she just said can we be mates but i rlly dont no what 2 do x