@bridensausage do you have kids, plural? If so when you had number 2, by whatever means, did it cross your mind you might not love them as much as the first? And Did it cross your partner's mind?
I think a lot of people do think about, it's normal. But how much one loves a child is very hard to quantify, or is it qualify?
There are lots of things to think about in parenting and, of course, if the OP's dh really doesn't think he can care fit another child and love them, then of course they cannot do this as a couple.
But I find the idea you might not love one as much as another to be an odd thing to be hung up upon. Because, how can one know?
I don't mean to minimise the OP's husband's position, but I think it is selfish.
One thing that persuaded me I could love a child not born of me was the fact I loved our pet hamster! Not even the same species!
Clearly no one should adopt soley beceacise they love their pet! But I also think no one should walk away, before an open day, because of fears of not loving as much as an existing child.
Because I feel sure that fear is natural to those who have birth children and I can't imagine anyone stopping at one birth child because of fears about future feelings.
Future abilities, like being able to care and provide, yes, of course, but feelings, it feels like a bit of a cop out.
OP maybe he really does feel one is enough and doesn't want more?
If you found out you were pregnant tomorrow, would he have the same fears?
Good luck.