It's a matter of trust. It's a matter of respect. It's a matter of communication. That is what defines a marriage. Not a piece of paper signed by a reverend, or filed in a county clerk's office, or determined by some arrangement as someone else suggested. These are the qualities that define a marriage.
So in any case, such as abortion, or any matter, you have to trust, respect, and communicate with your spouse. It's a matter of there being two people involved. I would have to say that in the scenario you described, I don't see a marriage at all.
I'll give you an example that is along the same lines, though not directly related. I want a kid, and my wife does not. So during sex one night I decide to pull out late to try and impregnate her and then shrug it off as "it must have been an accident." In so doing, I have broken the sanctity of my marriage.
I want a kid and she does not. So that just means we have to trust in each other, respect each other, and continue the line of communication to help us to decide together what is right, what is wanted, and what will ultimately be decided. Not go behind each other's backs and do whatever we want without any regard for the one we supposedly claim to love.