...the day after the scene between he and I, he asked me for money to make his car payment. I told him that all I had was my weekly $100.00 budget money in which I can do whatever I want to with it. He said, "Well...let me have that, it will help...but it won't make the entire car payment."
How ungrateful and demanding! It is not your responsibility to make his car payments. Especially when he treats you the way he does and shows no gratitude for all the help you have given him in the past.
I'm sorry he treats you so poorly. You don't deserve that and the best way to let him know you won't be giving him money is to just be honest. He's almost 30 years old and never going to learn to live within his means if you keep bailing him out.
It's time for him to grow up.