"Bijin de wo Kanemochi no Kanojo ga Hoshii" to Ittara, Wake Ari Joshi ga Yattekita Ken.

After a casual comment to his family, Iori Shino (virgin) suddenly became engaged to Tendou Tsukasa, a girl famous around campus for being rich and undeniably beautiful. But she was also rumored to be a loose woman who would "sleep with anyone." At first, Iori was confused by the difference between their knowledge and experience, But he became gradually attracted to her unexpected side... Two polar opposites question "the meaning of being in love." A slightly more mature romantic comedy! (Source: Kadokawa, translated)