Oh, how tough!
Does your DSS know that you are expecting? If he does, I bet that's 1/2 of
your explanation for his behavior.
What do I think is the right thing to do? I think the right thing to do is:
#1. To write a letter, and explain to your husband that parenting is TWO people job. In successful blended families, the biological parent steps up in situation like you describe. I'm not saying you should just give up taking care of your son, but his father and your husband owes both of you WAY more caring and understanding than he is showing right now. It is almost always easier for a biological parent to comfort a child in situations like this, and to explain that the fears are unfounded, than it is for a stepparent.
Try to keep it simple: I'm your wife, I deserve to be listened to when I am in tears, sad and devastated that the child we are raising hates me. I deserver more than you snapping at me, and telling your parents that I don't want to watch a kid that I've done so much over the years (How dare he?!). Your son deserves to be heard when he is scared and upset, simply because he IS scared and upset, and not because there is danger.
#2.If sharing the letter does nothing, I'd probably keep the bags packed, and present one of two choices - we go to counseling, or I leave.
On a side note:
I think the problems you are experiencing with your DSS are partially due to pregnancy, and partially due to him realizing that his parents are not together, but his dad is with you. It will pass, if approached with care and understanding. I know it's harder to say than to do (I KNOW
), but don't take it personally, because he is just a scared little boy. I cried soooo much the first few years of our relationship, and DSD had a weird love-hate relationship going on with me. It's almost impossible to realize that the kid actually loves you, but just hates the fact that the parents are not together, and you just happen to take up the place that is meant for a mom. I've learned to notice that kids say similar things to their actual parents, and it doesn't seem as threatening as it does to stepparents. It will pass. I'm sure of it. You could also try gently to set up little bonding activities for yourself and DSS. Plan something fun for just the two of you to do, and when he is calm and receptive - take him out for ice-cream, or for a bike ride in the park, or just visit some place special. Choose a calm moment, and ask him "Do you want to do <insert something he'd have hard time saying no to>?", and allow him to make the decision. He might say no a couple of times, but he'll come around eventually. Don't insist on anything, just let it go. Maybe start a messy craft project, and invite him to join, or even without inviting him, watch him approach with curiosity. I did that a bit with DSD, and it worked well in getting us back on track.
However... While I'm sure that your problem with your DSS is fixable, and simply requires time and understanding (from his dad), which he is not getting at the moment, I'm not so sure that you can change your husband into a caring dad and husband all of a sudden. Maybe he is just scared, like Jeannine says. Maybe you should ask him about it straight-forward? Assure him that you want this to work? If he is willing to listen and change - I'd give him a chance. If not - then packing and leaving sounds like not a bad idea to me. This marriage thing won't work when one of the partners just doesn't care that you are hurt and struggling.