It's not your obligation to achieve his life goals. I assume you were very, very clear and open about this BEFORE you got married?
A lot of how this will go will depend on how it was set up. The best case for you is that you've been clear and unwavering. The worst is that you didn't tell him, and so now it's new.
In the end, the back story only changes how the conversation goes, but not it's content or outcome. He can't force you to have his child. If he won't respect you or simple can't accept your choice, you both need to move on.