The progression of realization
Page 14: The reader's first glimpse

Page 17: Zen notices (hehehe... his precious blushing

)
Page 18: Oh my!

Page 19: Yae is a dense, dense block of ultra firm tofu

Page 29: Yae finally notices!
After the chapter: Are we the readers like... Zen's late mother, watching over our son and his childhood friend as their relationship slowly blooms? It makes me (almost) consider having kids...