When we met I always said I wanted children and he said he did too. I just assumed (stupidly) that if he wanted 'children' that he wouldn't put the brakes on at one
I think its entirely logical that OP would assume he wanted children and that would not mean "we have one child, and thats it"
Now he says he doesn't want more, and it seems he doesn't step up to family life either. Seems all the cards fall in his favour its all about what HE wants, and gets. Its devious.
Then again it could be they had one child and the reality of it made him feel "no more, one's enough".
I still think however that it leaves OP in an impossible position; assuming they would have a family of more than one child (which seems a pretty fair assumption to make in the circumstances) and now its no, we aren't having any more and thats that. So she has been put in her place. On top of that is doing more of what is required to maintain a relationship, than he is.
OP you are at least, a mother. If your need for another child is so strong it could break your relationship anyway. Whether you become pregnant "accidentally", or leave in the hope of meeting another man with whom to have a child, or even go via the sperm donor route. None of this bodes well for your relationship with this man either way. It really is a case of now deciding, do you want another child more than you want him. Thats the bottom line here
Its a tough call. You need to find a way to take some time out to decide.