Sounds really difficult.
I wonder - how does your husband feel about your pregnancy? I mean this gently and with compassion - but is it at all possible that having another child is your version of filling the emotional need that isn't being met by your marriage?
I ask because I was discussing this sort of situation with my SO recently. I wonder how often people who are having problems in their relationships look for outside solutions? Particularly to fill the emotional need that isn't being filled by the relationship?
For me, the worry is that babies, pets and other partners all need work, effort and time. And if your emotional energy is already being used up by a difficult relationship, is there enough left over for adding somebody new?
I once hastened the end of a long-term, loving relationship by getting a puppy. The relationship was difficult at the time and in need of work - work that neither of us knew where to start with.
I have always loved dogs and forced us into getting a puppy. The puppy hastened the end of our relationship - I just didn't have the emotional energy to deal with both the relationship and the needs of the puppy.
I hope you and your husband can work together to find a solution.