Chill. Don’t bring this topic up again with him, and focus on building your relationship and working out if he’s marriage material. Likewise - he sounds like he’s trying to work the same thing out about you, if he is still yet to propose.
You’re saying, ‘I won’t marry him if he doesn’t want kids,’… right now, that’s not even on the cards from what you’ve said so far - has he even proposed yet? You’re getting well ahead of yourself, and acting as though truly loving your dh and being committed forever to the man you marry in the future, is not as important as the chance to have kids with a random stranger.
Personally, I think the most worrying thing here is that you don’t love your partner enough to commit to him 100%. If you’re happy to leave him because of his ambivalence, then maybe you’re not as in love as you should be, to consider marriage.
Your expectations of life sound solidly set, and you may be setting yourself up for disappointment (That wasn’t supposed to sound like a Chinese fortune cookie!) 😂 Point is; one person is never fully in control in a marriage of two.
When the time is right, you’re all set up, both properly committed, he may really start to trust that you’ll always love him no matter what - only then will he imagine himself in a more vulnerable situation - and putting all his eggs in your basket, by getting married. Maybe then he’ll become broody. And if not, then, that’s his decision.
Right now, he rightly feels that you’ll leave him if he gives you the wrong answer, but, to his credit, he won’t lie, to tell you what you want to hear. What he needs, is to feel 100% stability and commitment from you - as he knows, that that’s the only environment in which chn can be considered.
Personally, I would rather maintain the relationship with my dh who I love dearly, than throw him away for the un-guaranteed chance of possibly having kids with someone else - a fictional person, who you haven’t even ascertained exists yet.
Life’s good either way, you’ve got to roll with it, and count the blessings that you DO have, not brood over the ones you don’t. 