They were together over 20 years when he confessed his infidelity. The other woman was carrying his child and she was putting pressure on him to leave his wife. This is how their marriage survived.
Many of us are unprepared to deny biology's drive after marriage. We see it as a weakness, a gross manifestation of our lack of faith and inner strength. We suffer this almost inevitable shame to eventually -- given enough shame and public penance -- be told it happens to good people and assured we can get through it if we find our path again and work together as a couple. There is no prevention where infidelity is concerned, only damage control. How do marriages survive?