Shaz, you have your LO. That is worth everything. And you just can't know what lies in your future - plus fertility doesn't stop, bang, at 40. It reduces, but plenty of people do have babies after that point, and you could meet and fall in love with someone else tomorrow. Well, next month, maybe. ;) But the point is, if your DH carries on being a cretin and this is permanent, you are still going to be able to meet someone, if you want to.
I also hate to point this out, but if the plan was for DH to be a SAHD after the second child and you the breadwinner, so he could write... you could be in this exact same position, only he would have been the primary carer, and thus entitled to remain in the home and remain the primary carer. You'd get the right to contact, and the right to pay child support. This really could have been worse, because you could effectively have lost your babies, too. As it is, you have your child, you're young enough to start again, and you are being canny about making sure you get the support your child and you deserve.
I agree that he probably wishes you'd be horrible, and that your refusal to be is best for our dignity, your child and your legal position.
So shitty that this is happening. I'm so sorry.