Polly - huge HUG.
I agree with the others who have said to try to get away for a couple of days & have some space to think about your feelings.
I don't know how your DH has convinced you this is the best for your other children - what does he base this on?? It sounds like a convenient guilt trip to me.
Right now your DH is being a bully, manipulative, insensitive and generally a proper wanker. I know he's calmed down some (Thank God), but it doesn't change the fact he wont talk about it and he wont go to councelling - which is the very least he owes you.
I don't see this as choosing between your husband and your baby (pregnancy?) - I fear he has done the damage already - regardless of what you now choose. Choosing to have a termination is in no way a guarantee you can have a 'happy ever after' after this, after his total lack of support, love & compassion - so please don't allow the thought that this is what you will get in exchange for the termination.
Something special has died - and this is something you really, really need to think about. I fear that no matter what you do, it 'could' spell the end of your relationship. Consider how you would feel if he leaves (or you leave), which could you best live with - a third child or a termination you were 'coerced/conned' into. If you end up on your own with the children - how much difference would it be if you had 2 or 3 children and would it be worth it??
You are not 'doing this' to your children!!! HE is (forcing you to choose). HE has - already (his treatment of you). There is NO guarantee that if you go through this termination for him (and have no doubt, it is what you would be doing, you had already decided if the MAP failed you would keep the baby)he/you will stay and the children will be with both of you.
Do not be talked into a quick private termination to 'get this over with' or 'to keep him happy' or 'to get it sorted' - please give yourself time to be sure you are OK with it, if you are going ahead with the termination.
However, as I said before and many others have said, you need to go and talk to someone who is trained to help you make this decision. Everyone, myself very much included, comes to this board with their own history/desire/beliefs and although it's invaluable to gather information, it's more important to talk to someone impartial in RL.
I am sure this is going to come across as anti-termination, and I'm not. I am anti bullying, forcing, coercing, guilting...
Biggest hugs, my thoughts are with you x