BNP appears to already know it can get messy:
I was wondering if you would ask your commentators, and say yourself, what an unmarried dad should do when he and his partner are splitting up acrimoniously? I am being as nice as possibly can be, but she is simply a woman on a hate mission. I wouldn’t care, but I love my son more than anything else in the world, and want to see him right. Indeed, I want joint custody. I’m not sure how to go about getting it though.
The first thing to do is to stay focused on your prime objective, which is to preserve the possibility of your relationship with your son. This absolutely does not mean acting servile towards his mother, but it does mean setting aside all of the anger and frustration you are probably feeling towards her. That relationship is dead, so don’t worry about it and don’t let her push your buttons. And while she does hold a lot of the cards, she doesn’t hold all of them. Money is always the big one, so make sure that you don’t play your only real card too soon and always make sure that whatever you give her is contingent upon her delivering her end of the bargain.
It’s probably best to preemptively lawyer up and get a consultation on what sort of rights and responsibilities you have in your state of residence. It’s unfortunate that the legal system will take advantage of your desire to do the right thing by your son, but that is the reality of the world we now live in.