Here is a moral dilemma.

You have two friends; Friend A and Friend B. You like both them but you have a deeper, more long term relationship with Friend A. Friend B wrongs Friend A. This has absolutely nothing to do with you, but you know that Friend A is really, really hurting. Friend A decides that they want to get revenge on Friend B. Nasty revenge, things that really hurt friend B and could potentially make Friend B pretty sick. You have told Friend A that even though you are sympathetic, you are 100% against the revenge scheme because it is just wrong, Friend B is so far unaware of Friend A’s actions so is not on the look out for potential land mines. Do you tell Friend B what Friend A is up to or do you just bow out and hope no one gets seriously (physically) hurt?