What's steps to take when dealing with custody of my son when we just recently moved back to my home state?

My 3yr old and I just moved back to my home state. His father had agreed to this move. I had addressed issues a little over a yr ago about his anger, controlling behavior, verbal abuse and some other things. This May (in front of our 3yr old, and 2 other small children, sisters and niece mother) yelled at me and told me to get the F out and other stuff. He agreed that if he didn't stay consistent with seeing his dr. and therapy that our son and I would leave. He now wants sole custody. I'm in IN and he in IL. What steps do I need to take? What grounds does he have to get sole custody after agreeing to the terms of our son and leaving? (He agreed to it 2x's) He has DUI's in his past, a me 1st attitude, doesn't watch our son well. Son has gotten ahold of utility knives under his dad's supervision, not watched and was down by a creek, and 3' behind my mower while I was mowing under his dad's watch. I'm trying to better ourselves and not loose my son. Please give me advice!! Thank you