@Qtpatootie,
So, your BF and you have 4 kids, been together 8 years, he doesn't want to get married yet wants you to put a good chunk of money into a down payment on a house that will not have your name on it because your credit is not so good and to top it all off, he goes crazy when you don't want sex and hits walls and slams cupboards and screams at you. He does this even though the reason you don't want sex is due to the complication from your recent c-section.
This guy sounds like a real winner. Honestly, I don't know what to tell you. To start, I would suggest that he needs some anger management counseling. You call his actions acting like a brat, but this is just rage. Bratty behavior would be pouting or moping around when you turn him down. What you describe is anger and rage that is only one step away from his striking you.
Maybe suggest to him that the two of you see a counselor and talk about what is going on. Because I find it hard to believe that his anger only recently began. Has he gotten like this before when you would not feel like sex? Or have you always given in to him because you knew he was prone to this type of behavior?