I think that even people who are reasonably relaxed about the idea of having a termination might find having one at 19 weeks unpalatable. OP says her ex didn't want her to have a termination, so having one at such a late stage must have been pretty difficult for him to come to terms with.
I'm offering no opinion or judgement on OP choosing to have a late termination - and I appreciate it's not what this post is about - but it's very relevant when considering the ex's anger and bitterness towards OP.
We talk a lot about women's feelings around miscarriage, stillbirth, and terminations, but there's not so much support for men. I imagine he's grieving for a baby he wanted and had no control over whether OP had a termination. I'm not suggesting he SHOULD have had any control, obviously not, but I can imagine he's still struggling very much with the decision OP took.
I expect the ex isn't willing to compromise or be reasonable towards OP about her share of the costs partially because he's still churning with all the emotions of the termination. Calling her baby-killer etc suggests that he's a very long way from acceptance.
OP didn't pay him half the cost for the goods/blinds at the time and now she's leaving and he gets to keep everything, it's not unreasonable for her not to pay him. She did contribute half of the bills/rent and that's going towards a property that he hopes to buy in five years.
It probably has left him in a difficult spot financially if he'd been budgeting for you to pay half, but if you're leaving it's not unreasonable to expect him to shoulder the cost. If you were feeling benevolent you could offer a token amount for the time you were there, but with such hostility between you and no likelihood of an amicable separation, you might as well just keep your money.
It's a messy, painful situation for all concerned and really OP, you just need to get yourself out safely, and then cut communication. Is there not anyone you can stay with for the next three weeks so you can leave now rather than dragging it out?