J.S.
I'm sorry you are hurting. I feel your husband was wrong for telling you that it was okay to try for #3 and then changing his mind. But, I also think that by not accepting his answer of "No", you are not treating him with respect either.
Have you sat down together and talked about your true feelings? I'm talking about a discussion where each partner is allowed to speak frankly and uninterrupted. Why is it so urgent for you to have a third child? Why is he so against it? You both speak your side, but make no decisions. I think you should let the issue rest for 6 months. Both agree to not bring it up until then.
And I would go back to couseling. Find a way to afford it. Good luck.