He said the car is his and he's entitled to use it and I should be glad he usually lets me use it.
I'm assuming this is your one joint car.
Given that, op, this is a HORRIBLE disrespectful thing to say. The fact that you haven't detailed your riposte suggests you said nothing, and that the both of you have lost the plot so much that you both think this was a perfectly reasonable thing to say. It isn't.
So.
A healthy relationship...
Both parties contribution is equally recognised. You have a child who needs full time care and thus one of you cannot earn any money. Thus it is absolutely obvious that the one who can, this is JOINT MONEY. The car is as much yours as it is his.
In a healthy respectful relationship his comment about the car would neither be thought nor said.
Let's just say it was said. Your response;
'No. That is OUR car. Don't you dare disrespect my contribution.'
LEAVE THIS VILE MAN. For your children's sake. And yours. Please.