A stepfather's courtship: A tongue crawling over soft skin

Storyline: A middle-aged man is seen telling old stories to a female high school student, Tatsuko. Tsuyoshi, a high school teacher, is staying with Inoko, the owner of a dried fish shop. Inoko, who is husbandless, seduces him and they have intense sex every day... One day, while walking on the beach, Tsuyoshi sees an unfamiliar woman in a uniform, Naomi, and cannot forget her. After a while, he meets her again, and they spend the night together, and he is confused by the reason why the young woman was used to men in the past. Tatsuko smiles as the man talks about Naomi and Tsuyoshi. What is the complicated relationship between them?