Sensei!

From Selene Scans:
It’s about a girl in high school, Hibiki, who falls in love with one of her teachers. The two start dating, but run into a lot of trouble (since they have to date in secret). Hibiki’s friends cover for her, and part of the story is also about them, too.

Side story in volume 1: Tomodachi Nante Iwanaide

Creator: Kawahara Kazune
Other Title: Teacher!
Length: 20 Volumes
Status: Ongoing
Genre: Comedy, Drama, Romance, School Life, Shoujo