In the intro, host Ira Glass discuses how some happy couples have no problem admitting that they got together because one or both of them cheated. You can see evidence of this in the New York Times Vows page, where newlyweds often use coded language implying that it took infidelity to bring them together. (Of course, they also want to believe that fate was somehow involved too.)
These write-ups will say that a couple's romance was a "bumpy road" or that they "encountered some obstacles." The episode suggests that these couples justify their infidelity by believing that whatever happened, everybody (including the exes) is better off because fate brought together two people who were meant to be. True or not, this is definitely a self-serving conclusion!
Do you think there can ever be a happy ending when infidelity is involved?