Let's say your wife was "approached" by someone you THOUGHT was a very good friend, and that person made some cruel comments regarding you... in an attempt to steal your wife from you. Let's say that your wife decided to not tell you about the incident and allowed you to continue to treat this person as a friend... and help out that person when he was down and out. Let's say that her failure to notify you of this incident caused you to feel like a complete fool.... and used. Was she being a "b*tch" or was she really just trying to protect you?
While I do believe there are times it is better to withold a comment to protect the feelings of your spouse, I feel that should be used for minor things, i.e. a haircut or a tie....
But, a wife's loyalty should be to her husband, and not only should she have torn the "friend" a "new one", she should have told her husband so he would be aware of how good a friend this guy was....
But, that is just my opinion..
It comes down to understanding where loyalties lie. A married man's first and primary loyalty must be to his wife, and to their relationship. You don't have a real marriage without that. And hers must be the same, or the marriage is in serious trouble, even if it doesn't seem so at the time. In this scenario, by remaining silent about it, she has compromised her main loyalty, whether she knows it or not. She has placed the well-being of her husband's friend above her husband's own well-being, under the false guise of "protecting" her husband. She's not protecting her husband, she's protecting his so-called friend, which means that at some level, she responded subconsciously to his advances. That spells trouble in capital letters, because when the truth comes out, the husband will not only feel like a fool, he will feel betrayed, and by the one person in this world that should never do so. That's a clear definition of being blind-sided, and I can tell you this from my own experience, there is nothing that hurts more than being blind-sided by the one you love. Betrayal is a nasty feeling, and it can set into motion a lot of unlovely events. I would venture to say that in many cases, a man's cheating can be traced to a betrayal of trust somewhere in the past on the part of his wife, and it may have been done innocently, with the best of intentions. By not seeing it for what it is, all kinds of problems can result.
All in all I'd actually have to say she did something good. Friendships are built on more than one thing, but can be seriously damaged by just one incident. But, especially given how we men are, if there's time between the incident and the reveal stuff like this can often be settled with a minor skuffle and some beer (he's buying though). Why screw up a friendship over something that will eventually become water under the bridge? Also time needs to be given to see what was really behind what he did, does he come back the next day and apologize wondering what got into him, or does he keep it up.