Divorced parents, evil stepmom, living with a friend?

My dad got married 2 years ago and 6 months later I moved in with them, I was 15. I had been planning on living with my dad for quite a while and his marriage was very sudden, he knew her for 2 months and I had met her once. She was awkward and quiet. Even all my friends and their parents asked me if she has problems. Things moved from that to her being mean. She blamed me for stealing and lying. Turned my dad against making us fight all the time and even convinced him I'm a bad person. She finally convinced him not to pay for any of my clothes or school stuff or sports. I even have to pay for doctors visits. She took away my horses and now i even have to pay to take lessons. The only thing my dad pays for is my car so i can get to work and a job. I love my mom but it's not a good time for me to be living with her as shes struggling financially and taking care of my grandparents. I've talked to my mom about it and she thinks it's unfair to have me move back to where she lives 3 hours away as I'm just about to start my junior year of high school so we are trying to figure out a way for my to stay where I am but not with my dad and stepmom. Is there any legal way I can do this? I have a friends family who has agreed to let me stay with them until college. And my mom has also agreed but what about my dad who is currently my guardian. If he agreed to let my mom have custody could she just say ok live with your friend and that's that? we live in Illinois if that helps...