OP, MN is the best place to come to if you want to be convinced that your relationship is doomed to failure.
By your own admission you are in a decent relationship on every level, something which most of the posters on the relationships board wouldn’t say of their own relationships. But because you haven’t come to an agreement on children you apparently should definitely leave him.
And now that you’ve talked about marriage and the fact you don’t want to that’s wrong as well and clearly your relationship isn’t going to work according to the MN masses.
In short, MN is only happy when someone is leaving/ending a relationship, and that’s the only answer you will ever get here.
With regards to children, you need to have a serious discussion. The reality is that many people, men in particular, don’t realise that they want children until they have them. The longing for a baby just isn’t the same in a man, and children represent a huge change in your life. He may not realise how strongly you feel about it because at the moment he doesn’t feel that way. But as you’ve talked about it in the past that doesn’t necessarily mean he’s led you on or that he’s about to go and have children with someone else.
Talk to him. Tell him that you’ve concluded that he doesn’t want children and that you feel that this means the relationship might not continue for you. After all, he hasn’t said in so many words that he doesn’t want children has he?
As for leaving to have children, think about what you’re leaving and what you’re setting out to do here.
You have a good relationship, you get on, he pulls his weight, you don’t seem to have much conflict, yes this is how relationships should be but the truth is that many aren’t.
So you leave and then what? Go on to online dating and spend a couple of years being pursued by creeps and being sent unsolicited dick pics until you’re fortunate enough to meet someone you click with? The “I left and am happier than I’ve ever been” anecdotes are the ones you’re going to get here because this thread is overwhelmingly full of people who want you to leave what for the most part is a happy relationship. But trust me this won’t have been the case for everyone. But no-one is going to admit that they left a happy relationship and ended up with an abusive narcissist but it was worth it because of the children they had.
And what if you can’t have children? There are no guarantees at this stage. Or what if the man you end up with can’t have them? Or what if you have children with life-long disabilities?
All these are just possibilities, but the reality is that you know what you have now and sometimes it’s better to look at what you have than paint a fantasy about what you want and what might still never be.
The reality is rarely the same as the dream.