I dont think you are being unreasonable OP or selfish, its not the changing of the mind, its the fact he is not communicating with you about.
If he had said actually I only want the one, you could have either come to terms with that or split. Instead he has been potentially leading you on for 10 years,
I also dont think you would be selfish for breaking up a marriage over this, because its not just about not have a second child, if he is unable to communicate his feeling regarding this, then what else is he not communicate on? Or maybe you are just not feeling like you are being listened to.
You could keep going on this path of, well maybe after this or this or this and wake up one day and you will have been robbed of your choice. He wont have been. That may lead to bitter feelings and resentment.
I would have one last conversation with him, sit him down and give him a date, you want to start trying, give him the opportunity to say no, I dont want anymore children. That way you know where you stand and can make a decision accordingly.
I agree with PP that the person who doesnt want kids trumps the person that does, but that doesnt mean you need to stay in that relationship, its a fundamental difference in how you see your life and unfortunately not one that can be compromised on