This sort of stuff is always going to happen. Being brought up in a high control group such as the JW religion, many folk get married way too soon just so that they can enjoy their nookies ASAP. Inevitably, once the novelty has worn off, they become vulnerable to thinking "Is this really the one and only person that I'm ever going to have sex with?"
Maybe if they'd played the field a bit, like most developing young people do, the curiosity and vulnerability associated with extra-marital affairs wouldn't be nearly so appealing.