You are separated. He is living most of or all of the time apart from you, okay. He cannot hear that he is hurting you, only that he is useless and failing to provide for you.
His father's voice is very strong and negative in his perception. Words like "it's over" and " he has no responsibility" are probably the words he heard form his father over the years as his father was overwhelmed and a poor example. Your husband has not taken the time to open himself up to those very negative thoughts and reason on them. He cannot, let me repeat that, he CANNOT hear your pain and fear as this will INSTANTLY became berating criticism. You are at an impasse.
What can you do?
State what you want as a positive matter of fact. He is the love of your life. Your child can grow to love him. You are good together, your life prior to this proves it. He is a good person who can overcome adversity. Feelings of fear and uncertainty are simply a way of checking in with ourselves that we are taking the very best way for us and our children. You will raise this child. You will support and mature this child to the best of your ability and it will be enough.
Sometimes getting across what you want in a way that makes him listen is to be fearful of the future and ask him as a stranger, would he be kind enough to help? When we demand help we sound like overbearing parents demanding accountability. Absolutely he is the father's child and this is his co-responsibility, but there may be no way to enforce that without his running away. Hopeful, there may be no way currently to make him come home and help you raise this child.
Trust you. This can be a paradigm where not only is his fear keeping him away, but the talks you have may also be projecting YOUR fears. Become introspective. How are you dealing with the possibility of raising this child alone? Can you see yourself alone in 1 month, in 7 months, in 3 years and still successfully parenting your child alone?
Going to a support group and listening to the struggles and eventualities of the attendees can really open you up to an understanding of what these supporters have gone through.
I have a saying. "One cannot force another to do a positive thing, force only begets a negative thing." He is hearing that he must take responsibility no matter how you speak to him. The problem may not be yours to repair or relieve.
Trust yourself until he is ready to be positive in your life.