So sad to think I'll never get pregnant again.

My husband and I have a 5 year old daughter and our son is 12 weeks old. He's very set on never having any more children but have felt the need and want for one more and then we can be done. I don't know how to feel differently about it. It just makes me so sad to think I'll never be pregnant again and I'll never have the 3rd child I want, I'd love for my children to have another sibling. Any advice on feeling better about this would be great. Thanks.