Everyone's entitled to evolve their opinions and change their minds as time goes on, including men.
He now speaks from lived experience - and your pregnancy and childbirth, the newborn etc etc experience may well be something he never wants to go through again. I wonder if there were challenges there?
The financial aspect may feel absolutely overwhelming, too ... Friends are now factoring in the cost of university to their decisions on how many they want.
You're speaking from a visceral urge to have another baby (that not everyone experiences), and labelling it as giving your child a sibling - as though somehow not doing that is a terrible thing. And he doesn't share that urge. His fathering is satisfied.
Although we get on fine my brother and I have always lived completely different lives. My childhood neighbour's two daughters were at each other's throats growing up. My great aunt loathed my grandfather and she and nanna were at odds for life. There's no Boden-catalogue guarantee.
You're in a different place now. You want. He actively does not want. It's going to get worse.
Do not 'accidently' get pregnant and present it as a fait accompli. Automatic fatherly fatherly feelings may not kick in, and this may trigger a side of him you'll wish had not been revealed.
Cajoling and persuading and showdowns and ultimatums may result in reluctant consent - but will colour how he feels about a new baby, and about you.
You'll find posts here from members who were themselves unwanted and unloved children. The spare.