Oh Tarumi.
You just know a part of her is going to think "If only I'd confessed first!" for the rest of her life.
But really I think Shimamura's line on pg 24 sums it up the best. Adachi would sooner die than say something like "Let's stay friends" she'd go all out constantly.
Shimamura's type is clingy girls I think, and Tarumi just doesn't fit.