Are affairs a good thing for a marriage? That depends on which side of the coin you’re on. It certainly is helpful for the cheater who gets all the fun, excitement and their ego stoked, but it is definitely not helpful for the the marriage nor the betrayed spouse who has to deal with all the emotional trauma that follows in the wake of an affair.
I know from firsthand experience that infidelity causes a lot of hurt and pain and can lead to divorce. While there are countless couples whose marriages were devastated by infidelity that went on to build a stronger relationship and a better marriage, it wasn’t because of the affair, but rather all the blood, sweat and tears that is involved in overcoming infidelity.