I personally don't know exactly how to handle this.
I didn't put my "baby daddy" on my son's birth certificate or anything, he get's my son when I say he can. He lost his privilages of keeping him over the whole weekend, now he gets him for a few hours on sundays. He know's if he doesn't listen to me and i go threw the courts to get him on his birth certificate and get child support that he would have to give me 4/5/6x the amount of child support I am currently getting (i really havn't gotten any yet, my son is 6 month old and when i found out his new "wife" is pregnant i told him i'm going for child support because when that baby comes my son will be screwed out of everything. Supposed to get his "child support" starting next month). With is new baby with his new wife he wouldn't be able to afford that.
Anyways sorry for me babbling...
If you do ever do seperate and you can PROVE to the courts that he is an unfit dad he can get either no visitation or supervised visitation if you wouldn't want him to be alone with your 3yo. It's a long process my not-so-normal way works pretty good, if only his dad knew how to be on time.
Goodluck
edit: sorry this was very unnessisary, i did not read other peoples replies first