Had he known that Daphne had such confidence in his decisions, he might have bored a bit to help him feel confident toward the decision he was going to have to make. Knowing that he ultimately had to decide, particularly when it came to children, he'd been driving himself crazy fretting over it. There was just too may factors to take into account and there was always one that would interact and cause problems with another. This wasn't Quidditch or even a case for work. There weren't clean cut lines to follow. He was on his own ... they were on their own.
He didn't think waiting would result in him missing out ... but he could be wrong. What if he took the chance and he did miss out? What if Daphne missed out because of him? He'd always wanted just a simple, ordinary life. Having a family would offer him that. Mr. Weasley had been adamant on that and it had left Harry feeling far better about the situation, but ultimately it would be Daphne who would help him through this. If she had confidence in him, then surely they could do this.
"You'll make sure I don't miss this all up, won't you?"