I applaud you and your husband for trying to work it out. I hope you get clarity about this soon. All three of you deserve to have the family founded in respect in order for love to grow.
That said, I have to write my opinion.
First off, I have to say that I absolutely disagree with Laura C. and Marci W. Women are under NO obligation to be subservient to their husbands. We don't have to tiptoe around them, we don't need to make them feel adored, we don't need to engage in sexual acts that we find repulsive just to please them, we don't need to wear makeup to bed so that they don't see us in our ugly state, and we don't have to be "barefoot and pregnant".
Yes, when we are in a relationship we need to work on it, but that has to be accomplished together. It is never all one person's fault. Sure, you are a perfectionist and critical, but what actions and behaviors does your husband exhibit that push these buttons in you? It really does go both ways.
I agree that you have answered your own question. You would not be with him if not for your son. Your boy is ALREADY aware of the anger and tension between you and your husband. All the medical, psychological and social research into relationships has proven that children take in a tremendous amount from their parents' interactions. And the likelihood of your son becoming angry and abusive as an adult is increased exponentially if he is exposed to your husband's mistreatment of you. And on that fact you will find no arguments from the medical world or the organized religion world.
You are financially stable. Think of how wonderful it will be for your son to grow up knowing that women are people too, who deserve to be respected by every person in their lives. Mutual respect is what builds a marriage, or any relationship, not kowtowing. Both you and your husband deserve to be treated respectfully, and if he has no respect for you, or you for him, it will never work.
As for the second child, I can totally understand how you feel on this subject. I, too, am 44 and have only one son (3 years old). I want a second child so much, but we just cannot do it emotionally or financially. I know in my heart that our son will be better off as an only child rather than with a sibling because he will not be exposed to undue stress in his parents' lives that would come from having a second child. I believe that your son will be better off as an only child if providing him a sibling is the only thing that keeps you in the marriage.