Growing up, a poor brother and poor sister share a room in a poor house. In a single room, there isn't much privacy, and early discovery leads to other things
His wife sent him to pick up a mattress that she had purchased. He found the mattress and a sex-starved teenager who showed him how smooth and comfortable the mattress was. That session made him late to collect his sister from the bus depot. She tasted his pussy smelling lips (no time to wash his face), and helped herself to his still sticky cock.
This is more of a thought experiment: What if the exclusion of a supposedly loved family member wasn’t malicious, or some kind of evil plot, but simply a genuine mistake? How could a family hope to mend their relationship? How could someone get past what had happened?