RENAI FUSHIN NA REIJOU WA REIKOKU KISHI-SAMA NO DEKIAI NI KIZUKANAI

One day, Countess Rosalie witnesses her lover, Hayden, cheating on her. Heartbroken, Rosalie becomes timid about love. However, she is then proposed to by the dashing future Marquis, Rufus…!? A school romance story between a love-challenged young lady and a notoriously cold knight! (Source: Flex Comics, translated) — Description from AniList community (anilist.co).