What jumps out to me here is that when he asked about a pre-nup you said no, you believe in sharing, but he clearly doesn't believe in sharing.
I think you see the three of you as a family, whereas he still sees you as independent individuals.
I get that he never said he was up for supporting the three of you financially while you stay at home. But he was happy to have one child and he is happy to have another, and happy for you to stay at home for several years doing unpaid labour which would have to be paid for out of your joint income if you went back to work, so I do still think he is having his cake and eating it. I think he twigged that your biological clock was ticking and you knew your best chance of having the children you wanted was to stay with him even in less than ideal circumstances, and he's taken advantage of that.
Clearly it isn't fair for the two of you to be paying 50:50 when he is earning a high salary and you are earning nothing. If you invested your savings in a property and he paid the mortgage you would at least have a joint asset and some security. I know you say you could live off your savings for 10 years, but what if it takes you 18 months to get pregnant again, then nine months of pregnancy, then a year's maternity leave? You'll have burned through a third of your savings. And that's assuming you find a job easily after 5+ years out of the workplace, which is far from guaranteed.
In your shoes I would definitely talk to him about managing your finances more fairly, but I would also try to get a job. I know you don't want to, but you have no financial security other than your savings right now, and you have no idea how long it will take you to get pregnant and have a healthy full-term pregnancy.