Boku no Sensei wa, Houkago Kawaii Konyakusha

Under a single roof, a teacher and a student secretly agree to live together?! Reina Sakurakouji, a beautiful woman, my teacher, and my fiancee?! And we're going to be living together in secret?! And also, Sensei is surprisingly defenseless and shy, so it's pretty cute! The story of a secret agreement to live together between teacher and student begins here!

(Source: Kadokawa, translated)