So how would you handle the other side of the coin. Like for example, if you were in my shoes, and it turns out an affair is happening, you saw the warning signs, and then your mother gets an STD, and confronts you about never telling her what you saw - what would your response be? Would you feel guilty? Would "it was none of my business" be a cowardly cop-out?

In other words I am looking for your reasoning as to why not saying anything would be the ethically right thing to do, so that I can understand it for myself. I want to feel that what I choose is right, but I need to understand it before I can feel it. I have to be able to explain it to myself and make sense of it.

Part of it is that if someone were cheating on me, and a loved one had strong suspicion but never said anything, I would feel extremely betrayed. If I got a disease in the process, I don't think I would ever forgive the person who didn't say anything. I would feel like they were just cowardly and not a true friend. So part of me is projecting that onto my own position.

What would be an explanation on how not saying anything is the right thing to do?