It seems like everyone is talking about emotional affairs. Check out this article: 12 Ways to Break Free from an Emotional Affair. (It's not written from a Christian perspective.)
Emotional affairs are tearing families apart. It starts with a seed of discontentment in your marriage or with your mate. It starts with thinking you deserve something you're not getting. It starts with comparing your marriage with others. It starts with a pattern of emotional highs and lows before your married.
Finding emotional purity before you're married, I believe, will lead to emotional contentment once your married.