I kind of like the abrupt ending here -- mostly because there's a dozen ways to continue from there.
Maybe I'm reading my SIFAS playing into it, but that "heart is held shut" bit seems almost like (if Kasumi is right) Yuu is becoming aware of her blockheaded protagonist status, and how she's been building almost-romances with between 9 and 27 girls (depending on if this is the game or a Nijigasaki-only world) -- and how she's got to stay playing cool and innocent, or she's breaking 8-26 hearts.
(Or maybe I'm just feeling guilty over leading Umi on, and making Ayumu jealous in both You's and Mari's bond episodes, and ...)