I think it would be best for you and your son to leave this abusive man. I think it vital to limit the ongoing damage to your son, as well as to yourself (it's child abuse to hurt you in front of him). However, please be careful about how you do this. When you leave an abuser is when you are most at risk of serious harm. My father said he wanted to leave my mum at times, but when she tried to leave he refused to let her go. I was scared for our lives at times. There were months of emotional torment.
I'd strongly encourage you to speak to Women's Aid and think about how to leave safely, anticipating worst case scenarios. Get legal advice, make plans, consider calling the police next time he assaults you.
One of the worst things for me was how no one in our house acted as if the violence was abnormal or wrong. My parents tried to act as if nothing had happened afterwards. I remember one time desperately wanting to call the police but being scared of how it would change our lives and of my mum not telling the truth, and what he'd do to me in that instance. I felt I couldn't talk to her about it. And then I was worried I had it all wrong because maybe he wasn't violent enough for it to count? I think if you can speak to your son and acknowledge what your husband did is wrong and not okay, and listen to how he feels, that could go a long way to helping him emotionally. It's so confusing and awful. You can feel so alone with it as a child in these households. He also likely is aware of a lot more than you think. Sometimes as a teen/young adult I'd wake at night to raised voices and stand by my bedroom door in the dark crying, not knowing what to do.
My mum is so, so much happier away from my father. We are all free now, and while sometimes things are still hard leaving is the best thing she ever did, for herself or us. A crushing weight has lifted. I don't think any of us have ever enjoyed life as much. So, it can get better. Really. You don't have to live this way.
Thinking of you and your DS. Stay safe.