I've recently been looking back at some of my comments on What Are Friends For? and find a large number saying that Greg was no friend to Eric, because he didn't tell him that his wife had given another man a blow job and came within an ace of being violated.
This begs the question what does a real friend do? Put yourself in the position. You know that your friend's spouse has cheated on them. The affair is over,and you've been told it will never happen again. You can see the offending party working hard at the relationship and the couple are happy.
A: say nothing but keep an eye on things?
B: tell the guilty party that you know and that if anything like that happens again you will spill the beans?
C: tell your friend that their spouse has been unfaithful and let them decide how to proceed.
I know that a friend of mine has been unfaithful. They had been going through a rough time but since the affair ended they are getting it back together and are happy. Do I have the right to change that? I ask myself what is to be served by telling the other partner what happened? They have children whom they both adore.