That kid saw the scene and made plans for his future. "One day that will be me!" He made a pact in his heart. I like how he acts as a reminder that Shou was once the eager little kid to her. She still sees him that way, even if he's grown in body.
We're all picking up how uncomfortable their relationship is getting, but I wager it's mostly their own fault. She's been putting her desires aside for so long she doesn't know how to express them- and that's led her to acting like his soggy doormat. And he's a horny little teenage monkey who couldn't tell that his partner was bothered. He was a slavering ape, for real.
If anything they owe that kid for pumping the brakes on them. It will give them time to think and acclimate, and communicate. They've got a lot of hurdles to overcome.
