That's why I compared to what Scripture says about confronting someone in the church that sins. First you go privately. If the person doesn't listen, then you bring someone. If still doesn't listen, then you go to the church. I believe it relates to his situation in that he has the choice to confront his sister, telling her she needs to tell his friend. If she doesn't, and she still continues seeing this other guy behind his back, then Blain has the obligation on going to his friend that is being cheated on. By not doing so, he's as guilty as his sister and other friend because he is essentially encouraging them to carry on with the cheating.