I'm afraid that many couples who leave the JW's will indulge in "flings". One or both parties may be tempted. My ex and I both indulged ourselves disgracefully when we left. The problem is the old forbidden fruit maxim, plus one's reason for not having an affair while a JW is the fear of disfellowshipping.
Once you're out it takes time for one's own real sense of morality to take the place of the WT brainwashing that we mistook for right behaviour. Some couples do survive and stay married, but I get the impression that the majority will split up. It's only when you're out that you start to mature and grow emotionally. I went through my adolescence in my late 20's!