While I'm away, readers give the advice.
Having been there myself, I think people should remember that telling the truth does not always make one popular or even appreciated. Consciously or unconsciously, those who do tell the truth may be motivated by a bit of a "savior" complex and may expect to be loved or seen as heroic for their efforts.
Well, the outcome is usually ostracism and anger. Not a rationale for not doing the right thing, but simply a caution: Your truth exposes one person as a cheater and causes the other great embarrassment. It may give them a better grasp on reality, but doesn't make them happier.
For my part, I've decided to trust my adult friends to make their own decisions, good or bad, and be there for them when things fall apart. It can be painful to watch these train wrecks in motion, but it is free of the overt judgments that breed resentment.
I was that friend, or a version of it, at one point. My husband and I started trying to conceive right after our wedding, marriage, but it took four years and
of medical intervention to do so. During that time, many, many of our friends did get pregnant. The most thoughtful friend of all wrote me a very nice card to tell me she was pregnant, because she thought I would want time to process the information privately.