There's this girl in my school that hates me and i don't know
why, we were pretty good friends at first but then for some reason
she currently hates my guts and i really feel like i could do
something to recover our friendship, what should i do?
If she doesn't have any reason to like you, then she don't need any
reason to hate you. 
The world is not perfect, you will only end up hurting yourself
if you chose to hold onto your perfect idealism about how people
should behave towards you.
It's true that many people are desperately trying to behave in a
perfect manner, living their daily lives giving model answers and
thoughts to themselves and others.
It's only a matter of time before their perfect world crash down
upon their own imperfection.
So what if you are trying to be perfect when nobody around you
are perfect?
Give up, and start to learn how to enjoy your imperfect life
until you can find happiness within your imperfect world
in the imperfect society.