I am not sure what to do first.

What is the name of your state?
florida
My boyfriend and I have been together for 4 years. We have a child together. He is 3. I cant take it anymore and want him out. The problem is everytime I tell him to leave. He says he will go but he is taking his son. He has no where to go but back to ohio and stay with his mother. I want him gone but I am afraid he will take our son and I will never see him again. what do I need to do ?

File for LEGAL physical custody of the child. Right now, if he is legally established as the father, he has the same legal right to custody that you do. If he is not legally established as the father, you will want to get that done, anyway.

Where do you live? Meaning, do you rent or own a home? Is his name on the lease or title? If so, he has just as much right to stay there as you do.