I'm going to leave my best friend of 3 years and she doesn't expect it
Why are you going to do that?
She acts so cold blooded, I don't like it.
It is understandable to leave a friendship if the other person is acting in that way. You can make new friends after ditching your old one.
Who does she think she is? She has no rights to be like that. I can do whatever the fuck I want.
You are absolutely right - you should spend time with people who make you happy. However, since you have known each other for such a long time, it might be worth it to try and talk to her about how she is making you feel. She might be going through something and might appreciate your kindness.