Is there ever a suitable reason for infidelity in a relationship?

DrWatson - I am not judging, but why is it easier to live with the guilt knowing full well that what is happening is wrong? Why not, decide if the marriage/ relationship is worth saving, if not leave and create another life with someone else. Often I hear people say they are staying because of their kids, why would they want their kids growing up in an environment where both their parents are forced to be together? Kids look up to their parents as an example, is this a good example?