Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am very sorry to know about this overwhelming reality you have been undergoing.
No form of abuse or neglect are acceptable or should be allowed at all, even less if they come from a close person who is supposed to respect, understand, love and support you. If y=to taht scenario we add the fact that you have a 4 months old baby, things get truly much more serious, it means not only you but yoru baby become victims of this serious abuse.
I sincerely do not think how things could improve when they have got so serious and abusive. Most times when victims of abuse try to confront in healthy ways the abusers, they could become even more victimized what never helps. The only effective and responsible option i see in a scenario like this is for you to immediately get all support you can from caring family and close friends to protect yourself and baby from him, to get away from this person and be safe. Obviously you would then file a report to police and get a restraining order if necessary in case he could try to harm you in any way (verbally, mentally, emotionally), but your family and friends would be there, so police if necessary.
This is very important since he woudl still ahve parental-custodial rights and from there he coudl try to manipulate and abuse you, while also neglecting and abusing the child , this is why most times, people in your shoes need to take necessary actions including police report and even restraining orders in order not to allow further abuse from happening. Unless he gets professional psychological support and after a while of hard work on himself he shows he has truly changes, not because of manipulative words, but because of concrete and consistent actions, then he could have a chance to get close to the baby, but until then -if that ever happens- you need, have the right and responsibility to take good care of and protect yourself and your baby.
This is not easy but tough, and necessary. You am your baby need and deserve a harmonious, happy and fulfilling life, safe and supported by healthy people around you, and never any form of neglect or abuse for sure.
Does it make sense?