Have you ever been the other woman?

I have often thought how the other woman in the marriage really does feel. Does she feel guilt over her affair with another woman's husband? Have you ever been the OW? Were you in love with this man?
A dear friend of mine died recently and to my surprise she had been the OW for many years and know would never have told me as my own marriage broke up due to the OW. At the time I literally hated this woman but it does take two to tango as they say.
Take Camilla for instance and the dreadful distress she caused to Diana, I wonder does she ever reflect on that?
Your feelings please.