Need advice on how to leave an unhealthy relationship. Help!

My fiancé and I have been together for almost 6 years. We have a 2 year old son and currently 17 weeks pregnant with #2. We are not happy with each other anymore. We fight and scream at each other everyday in front of our son I am so sick of it I feel sorry for my son. I want to leave and go back to my parents but he won’t let me especially if I took our son with me. He always stops me even when he’s the one kicking me out. I know I could sneak away while he’s sleeping but it would be hard not getting caught if I take our son with me because he might start crying. It would kill me if I left my son with him, I know he wouldn’t be able to take care of him. I’m the only one my son run to for comfort. Please give me advice on how I can leave this relationship. We can’t work it out anymore. There’s no more love. I need to leave with my son. Please I need help :(