Should I divorce or keep my situation as is?

My husband and I have been married 6 years. He knew about my son when we initially started dating. After we got married I became pregnant after 2 months. My son was 13 at the time. I noticed once we moved into his home, he was verbally and physically abuseive to my son. examples: turning the hot water off while he was taking a shower or turning the cold water off, tying his shoe laces of both shoes together in really tight nots, putting trash in his shoes, spitting in glass of water he had on his nite stand, putting broken glass in a gum ball machine, the list goes on. My son couldn't have his friends over and he couldn't go to their houses. My husband works for 48 hours at a time and then he is off for 4 days. So on the days he was gone, my son was able to be with his friends. One day, I came home in the middle of the day, I was tired and pregnant and decided to go home and spend some time with my son. My husband had my son working in the hot sun mid day shoeveling dirt and pulling weeds, 2:00 in the afternoon in 103 degree weather. When my son asked for a glass of ice water, my husband told him to drink from the hose outside. I told my son, to get inside and he was done for the day. I had a few choice words for my husband and of course he made it sound like he was doing my son a favor. I then told my husband he was to never tell my son what chores to do or discipline him ever again. On another occasion, I came home tired from work and ordered pizza for the family, I just had the baby and was nursing the baby when all of a sudden I heard some scuffling and then yelling and screaming for help and ran to the kitchen. To this day I can't take this image out of my mind. I saw my husband with my son in a headlock and my husband was punching and hitting my son over and over and over again in the head and the face. I tried to pull my husband off of him and he just kept punching him. I finally slapped my husband and told him to let go of my son. I told my son to go to his room and I would be there in just a few minutes. I had some choice words for my husband and he told me he was upset that my son was taking his pizza to his room. No food was allowe in the room and my husband had a fit. I told him to get out and he then reminded me that, that was his house and we should get out. He then went outside. I went to check on my son and asked him to call the police and report to them the incident and to pack a bag while I went to go pack a bag for me and baby. We waited for 2 hours and the police never showed. I got my children and left and went to the police station to file a report against my husband. We then went to a hotel and spent the night. My son was complaing of a headache and I took him to emergency where we then found out he had a concusion. Child protective services came to chat with us and I was told that if I didn't take my children out of this environment. They would do it for me. Make a long story short, we moved out, I bought a house and we have been in our own home for the last 5 years. He rarely comes to see our baby, now 5, doesn't help with purchasing clothes, daycare or food because in his eyes, I am the bread winner so why should he help. I asked him recently had my daughter's birthday party and 3 weeks prior I asked him to help in paying for the party. He told me he would. I told him time and place of the event. I didn't hear from him again until the day after the party. I knew this would happen and had even discussed this with my mom and a friend of mine. He yelled and screamed at me that I didn't "remind" him and that I should have called him. I let him know that if he was so concerned then HE should have called, knowing that her birthday was coming up, he should have made the effort to see if I needed assistance or to verify when and where. Of course, he contiued to blame me and said I was trying to keep her away from him. I don't divorce him because I don't want to have to end up sharing custody because I don't want her to have to go through his abuse. He believes in spanking and hitting and making children fell that they are beneath him and I just can't do that to her. She is 5, head strong and I just don't want to break her spirit with his abuse. But, I am lonely. I do it for my children and really if I have to chose my happiness for theirs I do it for them. I am tired of him putting me down and making me feel like I am in the wrong, but don't want to risk having to share custody. What to do?