Dad’s Thick Fingers Playing With My Wife’s Private Parts

After his mother dies of cancer, the protagonist takes his depressed father into his home rather than leave him alone. A drunken celebration for a work promotion ends with his wife, tipsy and affectionate, sleeping with him right there in the house with his father a room away, and that one lapse is the hinge the whole story turns on.

The father can't shake the mood from that night and keeps drinking trying to get it back, sliding deeper into depression instead. Then the protagonist is sent on a week-long business trip, leaving his wife alone in the house with his grieving, increasingly unstable father, and the story picks at what happens while he's gone.

It plays as a visual novel told from the husband's side, with choices steering how far things go and which of several endings you land on. There's no pretending the outcomes are all comfortable ones; the branching exists specifically so some of them aren't.