How could the biological father of my son get visitation rights?

Ok here is all the details.. The biological father of my son was an abusive, pothead that I finally got away from when I was like 4 months pregnant. I thought he would change once I got pregnant but it only got worse. After I left him I met my fiance and he has been the father to my son ever since. He was in the delivery room and everything and he is everything I want in a father for my son. Recently the bio dad has been sending me messages that he is going to go to domestic relations and that I was going to be taking my to court. Also, he's not on the birth certificate and I have never tried to get child support from him or anything. I told him that he's not the father. Also, he lives at home, smokes weed constantly and makes doesn't have much money. Would it take him a lot of money to get me to go to court or could he do it without a lawyer or is there a place that will help him or something. I live in PA. I don't want him to ever even see my son. So, with his situation do you think it's possible that he could or would it probably cost him too much money?