Waltz with a Black Cat

From DMP:

Haruka Iijima and his teacher, Nakagami Sensei, are in the middle of a bitter-sweet relationship. Being a student and teacher couple isn't easy, but they're about to find out that's the least of their troubles. Nakagami Sensei's family, the gang of impossibly beautiful, age-defying Nakagami Sensei obsessed individuals might just turn out to be the worst nightmare. Will this love be able to survive the perverted mystery that is the Nakagami Clan?!

In the series:

V.1 - Nakagamike no Ichizoku

V.2 - Akuma Kiru

V.3 - Kamenbutoukai de Aimaseu

Included oneshot:
Kuroneko to Waltz (Waltz with a Black Cat)
Hirose is mad. Once again his boyfriend Matsui has cheated on him, with the sorry excuse of: "Sometimes I wanna see a girl's boobs more than a guy's d*ck."
Crying at a nearby shrine, Hirose curses Matsui... And the next day, outside Matsui's apartment, he finds a black cat with a scar just like Matsui! And Matsui seems to have disappeared...