Maybe the affair-or the POSSIBILITY of one-serves as the "kick up the backside" that is needed to end a relationship that is already long dead. The children may be grown, there may be no love, no sex for 5,6,7 years;the "glue" that should hold 2 people together is no longer there. Even those of us who would not normally consider such actions may take that path in an attempt to find a way out of misery. To be a 'serial' adulteror-yes ,that is immoral, but the search for a tiny bit of happiness can result in actions that would not be considered otherwise.