I could also relate to your poem. I have seperated with many of my friends for stuff like that. but afterwords i realized that i need those friends. In your last stanza you said:

why did you let this happen
you let her take over
and i cant be your friend
if she's also another

I think that you shouldn't look at it that way because it would make her feel like she has to choose. My friends had made me choose too and it sucks. believe me she will get sick of her being mean to you and it wont last. Its just a phase. You probably have a lot of mixed emotions too. This year is my first year of highschool and many things are changing including friends and it is very hard also but I am trying my hardest to stay strong. I wish the best for you!