This situation is hurting the child. It is hurting you too, but the kid comes first in this. If you have legal custody of the child, take him, get out, get a lawyer. If you don't have custody, call CPS, or find a sane family member on your husband's side that can take him in.
BTW, I know someone that was in a similar situtaion. Her husband had custody of his grandson. He was abusive, and she stayed to take care of the grandchild (again, not her relation at all). One day he said, "it's the kid or me."
So she left :7 adopted her step-grandchild, and the creep is out of the picture because he was dangerous to the child. She's a hero, in my book.