Kimi ga Ita Toshoshitsu

The protagonist is a third-year college student. He's been placed in charge of the library and stays after hours. That's how he meets a lone book-loving girl. His job and her passion lead to deeper conversations...

... But they're not the only ones talking. A popular and well-known freshman is also after her. "It's strange to only read books.
You need to experience more of life.Don't you want to do what normal college girls do?"

From a small misunderstanding, a crack forms.
Slowly but surely, her mind and body are pried open...

[From DLsite English]