I can kind of understand what you are going through only because I have heard this same complaint from my boyfriend.

I always thought I would want another child as soon as I was finished with school.(ironicly nursing school)
well now that I am nearing my graduation I am thinking... maybe I want to go on and become a nurse practioner?
I brought up my doubts with my bf and he got upset. He always wanted to have at least two kids.
We already have a 2 year old together so I am in a different situation here but the point is that people usually don't change their minds about these kind of issues for no reason are you guys going through any kind of change? Or did he not want to have kids in the first place?

How is he around the children you know?

I hope you can figure out why he changed his mind all of a sudden. I know I wasn't much help but your feelings really struck me as exactly how my bf must be feeling [Eek!]