so my crush already have a bf :( and her bf is my friend..i dont know what to do anymore,i've been chasing her like months.
I also had a fight with my best friend and he block all my contacts.. i want to change school..

Your life isn't a mess.
You've just embarrassed yourself by playing victim to your own feelings or thinking you're entitled to something.
Next time try not to let your feelings go to your head.
No matter how long you 'chase' someone, you never have the right to think they'll show anything back.

Changing school sounds like a decent option if you've fallen out of the normal social flow. Just make sure not to repeat the same mistakes at the new school.

Or carve out a new path at the same school. One without the girl you like and without your best friend. There's no shame in living a life for yourself rather than others.

Ultimately you should wait until you've found a group of emotionally mature people (or at least one emotionally mature person) and attempt to cultivate meaningful intimate and romantic relationships with them. The fact you're at school could potentially say a lot about the emotional maturity of the situation.

School makes up an important but small part of our life: you shouldn't worry about it more than you have to. It's primarily an area for education, and any role it plays as a social influence should be a secondary one.

I recommend joining clubs for social bonding, like card games or music.