Jane A. Smith
What does regret mean?
Regret involves guilt, feeling bad about something and to perceive it as a loss, but analyzing it from its polite point of view we find that it is used when expressing sorrow and most often to apologize or deliver bad news.
For those hurt by infidelity, the pain and disappointment are so deep that apologies as a polite expression or in its natural sense are useless and unappreciated. Thus, the ones who cheated will not feel loss, but a great pain seeing their partner down, hurt and possibly crying. Loss will occur later on, when they find themselves alone and wake up to reality.