Back in the dragon pit, everyone chastises Jon for his inability to lie, including his queen. But the King in the North makes a good argument for why it's time for people to start telling the truth. The Night King is a threat that requires strong alliances that aren't built on lies. Also, he simply can't pledge himself to anyone other than Daenerys. She's still a bit miffed, because as she reminds Jon, she lost one of her dragons in order to secure a truce with Cersei, and her dragons are the only children she'll ever have.
Interestingly, Jon isn't convinced the witch that told Daenerys she'd never have children is right. His comments seem to suggest that season eight could bring see the Mother of Dragons with a baby on the way. At the very least, his words appear to make Daenerys think about how quickly she accepted the prophecy as truth.