KONYAKU HAKI SARETE JIYUU WO TENIIRETA ONNA HAKUSHAKU DESU GA, CHISHIKI WO IKASHITE SHISHO NI NATTARA OU OTOUTO DENKA NI MITOMERARE, SENZOKU NI NARIMASHITA

After breaking off her engagement with her fiancé, Karliana makes a fresh start and becomes a librarian at the royal library. One day, a seemingly frivolous, handsome young man named Dietosius appears before her. Impressed by Karliana's intelligence and thirst for knowledge, Dietosius asks, "Would you like to become my personal librarian?" (Source: Compass, translated) — Description from AniList community (anilist.co).