@miyako19 that's why i said in my imagination. I abhor polygamous relationships based on sexual interest. I understand poly irl is often messy and used for one's own gain, treating their partners like something belonging to them (as they would buy their way into marriage).
But i like to think, in a happier world, 3 people can have a relationship simply because they love and care about each other very much. Beside, i never think of my sumire-kiyo-kenta ship in sexual, 3some way, i just think about how kenta and sumire going home after work, greeted by kiyo and her amazing food, and then they ate dinner together. The spiciest i imagine was just the 3 of them holding hands while sleeping.
Also this discussion got dark for such a wholesome manga I'm sorry about that