I don't see any problem in someone confronting the other person if they know them.
Say if it was your best friend, or sister then you might feel betrayed by them as well as the dude.
In the Scandal instance, while they aren't close friends, Liv is smiling, hugging and laughing with the wife while she bumped uglies with him on the side
My friend did this when she had her affair. The wife really, REALLY liked her and tried to befriend her. They hung out a couple of times and chatted fairly regularly, sometimes about her husband.
When it all came out Wife lit a fire under my friends *** for being so fake. I think she deserved it
Wife was worse with the Husband, even gave him a beatdown, but still definitely had some choice words for my friend.
If it is a completely unknown person, I don't think they should be confronted in most cases. Its just the partner who deceived her and lied to her face.