Advice question

I am really struggling and trying to figure out so many things right now! I am 5w1d pregnant and my partner is leaving and does not want me to keep the baby 😞 He is my ex husband and we have 2 children together already and a previous divorce agreement of 50/50. I am asking for knowledge on custody, what is he allowed by law? Can he get partial custody of a newborn? Can he have custody when I’m breastfeeding?? I am just so overwhelmed right now in a time I should be calm, excited! And Kaiser won’t see me until the end of June so I have to wait so long to see if baby is ok?! 😭