Maybe he just finds the idea of having children too awful to contemplate. I know I do, and I am female. There is basically nothing at all about children that I like, and according to my parents, that hasn't changed since I was a child myself.
It sounds like unfortunately when he talked about having children, he was just doing what he thought he needed to do to maintain the relationship. If you can't imagine a future without him, I guess you will have to see if you can imagine a future without children (and possibly marriage too). I think it's true to say that a lot of us find big displays of emotion overwhelming, and tend to run away when this happens, so perhaps give yourself a couple of weeks before you try to talk to him, so it can all be a bit calmer.