Hi, I work with a violence against women partnership, I can hand on heart say that this is domestic abuse.
You are NOT to blame, nor should you feel ashamed in ANY way.
There is a false narrative around DA that it is an anger thing for him, but there is a reason this happens in private, these men are very in control of their emotions and know what they are doing, so I'm not surprised there is no anger.
His abusive behaviour likely started long before you even met, in previous relationships (you can ask for a disclosure on this through the police, Claires law in England and DSDAS in scotland)
Of course you feel love for him, I'll almost bet that he moved very quickly at the start of the relationship, showering you with love and affection and telling you it was forever from very early on.(Lovebombing) also a known tactic of abusers!!!
It's also what draws you in, you see that loving man that you met initially!!
If you want to see how controlling he is, the best question to ask yourself is 'what am I not aloud to do?'
Another thing, YOU haven't subjected your son to anything, your husband has. Even as a step parent he makes a 'parenting choice' when he perpetrates the abuse, HE exposes your son to it, not you!!! I have no doubt you work very hard to protect your son from it.
All the comments on here saying you should just leave, why did you get pregnant etc.... don't listen to them, that is victim blaming at its best. The question we should be asking is 'why doest he stop abusing you?'
My lovely please please seek help through a women's aid charity in your area. Remember you are the expert in your situation, you know him and his patterns better than anyone else. Womens aid will help you to do what will keep you safe!!! Good luck, you're stronger than you realise!!! ❤️