That's understandable. Since I don't know what the manga adaptation will omit, I don't know what in it will be next. But, in the light novel,
[ul]Shimamura and Tarumi become reacquainted;
we learn that Shimamura had been deeply important to Tarumi;
Tarumi, essentially unaware of Adachi, begins a very careful courtship;
Adachi, vaguely aware and frightened of Tarumi as a possible rival, expresses herself more plainly to Shimamura;
Adachi and Shimamura begin dating, with poor Tarumi oblivious; and
Adachi and Shimamura will be together years later.[/ul] I don't know what comes of poor Tarumi's heart.