S1·E5 Ring of Water

Makoto and Kotonoha go to the pool for a date on the same day as Sekai and 6 of her friends. At the pool, it's clear that Makoto and Kotonoha are dating, however it seems as if Makoto has developed feelings for Sekai, hinting her that he wants to be with her instead. Sekai keeps reminding him that he's Kotonoha's boyfriend and cannot be with her, and tells him to forget about the "practice".