If you really love your husband and want to make it work you should definitely stay. If both of you are working hard and saving money to move out and get a new car I don't see why you shouldn't stay.
You guys will overcome the situation, it will take time and a lot patience but once you're out of HER house you will definitely appreciate your privacy and love each other even more. Just keep on pushing for your husband and little son. You guys will be fine