I know it's really difficult when you are desperate to conceive your baby, but guys can be so insecure - there's so much pressure on them to 'deliver the goods' - and it's no wonder that sometimes that can be overwealming. As I said, I know it's difficult, but if you can try to think of ways (physical and verbal) to reassure him that you think he's sexy and you want to be with him not just for what he can give you, that's a pretty strong aphrodesiac...
HTH and all the best for you both.