Thanks everyone for the input. I am reading it all, and pondering.
I would like to point out that I am not threatening to end my marriage and hysterically gnashing teeth and wailing. It is not an ultimatum I would put to dh - "another child or I leave" - not really the way life works, is it?
Justa - yes I do most of the hands on stuff, and disability stuff. That's how it works for us, dh is out full time etc etc.
I think Coldcomfortfarm has it closest. While we were in the postponement phase of dc3, while all the statementing shit was at its worst, and we were at our lowest point wrt the grieving part of dd1's disability, dh's answer when asked about more children was always that he'd love more, try soon, etc. It is a sudden about turn for him to be saying absolute final "no"
As to why 3, and not go on for 4 etc. Well, 3 is what we always both thought. We are both one of 3. 2 doesn't seem quite finished.
I think if I pressed dh on this, he would admit 2 seems unfinished, but go on to cite the going to back to babies being hard, too old, etc. That's what not fair. He has never indicated this before, and I would have been happy to have one earlier, so as not to exit the baby phase - that's where Tue feeling of being strung along has come from.
Yes, we have had our issues, what couple, faced with what we have been through, wouldn't? Overall we are ok though. But this feels like one more thing for me to compromise on, not him.
Obviously we are feeling some effects from e economic climate, but really, this is not really an issue for us. Dh's job is secure, and he earns a very good wage.
My step children are older - both adults now. I can't see that there would be any great closeness for dd2 when she is older - they are 17/18 years older than her. General relations are good though.
Oh, and whoever posted about hoping for an accident each month due to contraception used? (sorry, can't scroll easily as am on phone) that's us. Dh uses condoms, well he doesn't, as he prefers jot to so relies on withdrawal.
He wouldn't blame me if I got pregnant, or expect an abortion. But it messes with my head, a LOT. I find myself hoping each month for something I know dh doesn't want. Not to mention feeling used just cor sex (a silly feeling, but it is what happens).
So yes, a lot going on I suppose.