Can I move in with my step dad?

Alright, so, I always got along with my mom. Well, other than when I was little, you know? But now that I've matured, even though she still punished me, I would always know it was for my own good... after awhile. My dad, on the other hand, is crazy. Him and my stepmom go over the top on punishments. Now my mother passed away. I became a little depressed. My grades slipped. My dad took me to Joplin, where the tornado hit. I had to work with him. This was to teach me a lesson. Not about working hard or to give back. IT WAS ABOUT HOW BAD IT WOULD BE TO LOSE SOMETHING YOU LOVE. 1 MONTH AFTER MY MOTHER DIED! He's going crazy again, and I want to move in with my step father. He married my mom, but they didn't think to have him adopt me. Well he has no custody anymore so my dad thinks he can walk all over me. To give you an idea, I left my dad's house 5 times during the school year because I couldn't take it. Twice for months at a time. I'm 15, almost 16, and I live in Missouri.