How do I obtain sole custody of my son in mahoning county ohio?

I am a young mother living in mahoning county ohio. I have stayed at home and taken care of my son and my ex fiances daughter for 4 years now. I have tried to make things work, and help the father of my son out, for years. He is addicted to oxys and lies, wastes away all of our money and wants no responsibilties with the kids. I take care of them while he is dope sick or doing whatever he wants. He refuses to even watch them so I can work. At this point I want to end this, and get sole custody of my son, so I can move back home to Connecticut around my family. He hasn't been violent but threatens too, and even has raised his fist to me. He clearly states that he cant stop using drugs and doesnt want responsiblities, and the ids would be better off without him. But I know if I have to file for sole custody he will fight me on it just dispite everything. I cant even trust him to be able to watch my son. What do I do? I dont know where to file, or how, and cant afford a good attorney. Does anyone know the laws in Ohio? Or what my chances are?
Thank you