toxic relationship

i would really appreciate some advice. i have a best, best friend that i met in 9th grade (i just started 11th last week). i've only recently acknowledged to myself that she does some things that i just don't agree with and don't feel are characteristics i need in a friend. i'm not even going to begin to tell stories of what she's done, but i will say this. she and i are well known around school to stick close together and be loyal to one another, etc. but shes shown me the past 9 months that she doesn't care about others and she has an unhealthily inflated opinion of herself but i think its because she's incredibly insecure. i dont want to diss her in any way but i can't agree with parts of her lifestyle. i also feel like she truly does care about me but at the same time i feel used and like i live in her shadow.

if it were easier i'd distance myself from her but i just don't know how. we have classes together and see each other at school and cutting off/lessening our contact would be so, so hard to do. i've tried talking to her about this and somehow she manages to make me feel like it's my fault or all in my head. she never wants to resolve anything and acts like i should just submit to her.

please help me bc i feel awful all around and her mistakes or decisions are negatively impacting me. i don't know what to do