Nukarumi no Shokutaku

Mia, who works part-time at a supermarket in a town in the countryside, is having an affair with the manager. Mia loves the manager, who is kind to her, a woman with no redeeming features. But suddenly, he tells her he's breaking it off. The reason is his wife's depression. The manager's words, that he can't continue their relationship because he needs to spend more time with his family, fall on deaf ears. She ends up deciding, "I still want to be happy with the manager." With that thought, a household gets dragged into the mud.

(Source: Shinchosha, translated)