Partner wants to move

This is a bit harsh.

You could say the same about OP. It's a normal thing for couples and families to consider

I wouldn't move now because doing it with a small child and baby on the way is just too much hassle, but a few years down the line he's within his rights to bring it up again.

No, don’t move. But if he decides to without you then what?

So the pull to his relatives is stronger than to you and his dc? Cut him loose op.

I wouldn’t move. If you do and you become isolated and can’t settle, you might be stuck. If your relationship breaks down, he might obtain a court order saying you can’t move away with the children, so you’d be even more stuck.

YANBU. So many women get worn down by guilt and pressure that they move to where their H wants to go. The H doesn't feel this guilt about what they are asking of their partner.

Don't go. Frankly, he's being selfish, and clearly prioritising himself over you.

You'll regret it if you move and the resentment will kill your relationship anyway, so you are better off staying where you are.

How often goes he go to visit his family currently ?

"he's saying being this far away is slowly killing him."
He's going to have to come up with a bit more detail than this! What does he think will change for him if you move closer to his family? What does he think will change for you? What life does he expect to lead there that he can't here? What will he do for a job?

I'd be wondering, since you have one child and another on the way, if he's coming under family pressure to move 'their grandchildren' closer to them.

How long ago did he move to your area and how long have you been together? Has he ever so much as hinted before that he wanted to move?

TBH my default answer would be no, he'd have to put up very good reasons to move you all, and 'it's slowly killing him' is not any sort of a reason it's just emotional blackmail.

Would halfway ever be an option? I understand your logic of him being there already when you met, but I'd be so upset hearing my DH was so upset about it - slowly killing him sounds like it's having a real impact. I don't think it's a case of who's in the wrong or right, I think it's a case of what can be done to help both of you if it's possible.

YANBU. You met where you are now and you've always been honest about it being important to you. He's the one moving the goal posts.

Incidentally if this relationship breaks down are you able to support yourself financially?

YANBU. I wouldn't move either. I think if you'd met elsewhere and moved to be closer to your family etc I'd consider it, but you met him where you live already. Has he said what's changed?