Why does my mother defend my abusive dad?People who are abused for a long time often have no objective understanding of their situation. When in such a situation, one way of coping is to tell yourself lies like, "He's not really a bad person," "It's not that bad," "It will get better," etc. Often the victim will blame herself because she has become hypersensitive to her own flaws through repeated abuse. If she believes that her behavior (or, as you describe it, your behavior) can influence his rages, then that could provide her with the illusion of having some small control over her own life.
It sounds like you are very angry with your mother as well as your father, and maybe you blame her for allowing the two of you to continue in this situation. But you cannot make her decisions for her. Your responsibility is for your own life just as she must become responsible for her own.
Your father is using a common tactic of abusers when he puts you in a situation where you are financially dependent on him. That's how he exerts control over you. And abuse is always about power and control.
You will never thrive while you are under his control. The time to get out is now. It will only get worse. Find a safe place to go, and get out. You may have to put off college for a few years, but you are young, and you will catch up. But staying in this situation will drain you dry. This path only leads to heartache and failure.