This post might come across wrong but genuinely not trying to trivialise how you feel.
I think you should stop and really consider if its more the idea of having children you feel strongly about or having them. I have 2 children so I am doing a bit of 'I'm alright Jack' but I can honestly say as adorable as my children are, I sometimes look at the state of the world as well as the personal sacrifices I've made and think if I knew then what I know now, I wouldn't have had kids.
Before I had children I never really experienced fear for anyone but myself, but now I find I have that emotion in regards to my children often, and it is an extra burden that fear.
Of course the world would stop if everyone stopped having children for the above reasons. But it's not just that. It's all the time and committment and the way having children really changes everything. Having children is a greater responsibilty on women imo.
I think if I'm honest, I've had children for 3 main reasons. 1. Strong biological urges 2. It's something people do and society expects 3. It's something women are expected to do and tend to feel crap if they can't do. I'm not sure on that last point that it's the same for men. I don't think they feel having children is tied to their manhood in the same way it appears to be for women.
The biological urge to have children is hard to ignore, (at 40 mine is ringing hard despite me having 2) but is it really reason enough to have children? I question this. I've had months of strong baby brooding where I just want to go on instinct and I almost feel like having a one night stand to get pregnant, but then when it dies down, I find myself thinking the last thing I would ever want is another baby and its hard for me to reconcile the two different states.
I think you ought to realllllly stop and question why specifically you want children, are any of the above factors responsible for these feelings? Before walking away from what seems a great relationship. Then if you decide you must have children, fair enough by all means walk away and find someone else, with no regrets. It just seems like you a bit torn.
Of course this is easy for me to say having kids already, so sorry if this post offends, and ignore if you want.