My mother is annoyingly loyal to my father?

My mother annoyes me sometimes because she's on my jerky fathers nuts when he doesnt seem to like her. All my life my parents have argued and fought and I mean ALL of my life. As a kid I remember my father not even coming home for days I guess because of her...I've never seen them show any affection before, not even a hug... And i even saw him atrack her once...But yet my mother is on his nuts. If I'm doing something she will rush and tell me to hurry up for him to take my place or when he punched me in the stomach for nothing she goes "you deserved it" when I'm laying on the floor and I can keep going on. She acts like hes a king when a) he is a jerk b) he doesnt like her. Why do you think she stays with him and acts this way towards him? Does she have low self esteem. Is she delusional? Why's the deal?