Child custody while soon to be divorced?

Me and my "husband" have been married for 4 years and have a 3 year old child together. We are planning to divorce, however I currently live with him. I have a place I can stay that is safe, and clean with a friend of mine. My "husband" tells me I am not allowed to bring my child anywhere, not even to the store to buy him a toy and he must come with us. We live in New york state and I am not sure of the laws here because I am originally from Ohio and only lived in NY for 3 years. I work a full time job and was always a stay at home mom up until we decided to divorce because I am trying to save to get my own place. I am going insane living here and he continuously threatens to call the police on me and say I am kidnapping if I want to just take my son to the park or anywhere else. I have never been arrested, in trouble with the law or on drugs. The only thing I can say is after my pregnancy I dealt with postpartum depression for about a year. I want to get out of here even if its temporary but I cannot live without having my son. Am I able to take my son where I want so long as I bring him back? I work full time so the little time I get with my son is cherished and I dont feel I should have to bring my "husband" with me everywhere I go. He constantly screams at me in front of my son and I cant handle it anymore but I dont want to lose him. I plan on going to the courthouse this week to file for temporary custody until the divorce begins but I dont know what else to do. PLEASE HELP. I cant go days without my son but I also cant continue to stay int his house being treated like a prisoner with my own son.