Decades of observation has led me to believe a wife's reaction to her husband to be the best predictor of lasting love. A woman who makes sour faces when her husband is nearby or when her husband is talking, or who mocks him especially in public, reveals the disdain that will likely end the marriage. Likewise, a woman whose face lights up around her husband, who shows some pride in him when he talks in groups, and who is playful with him, is indicating the proper attitude to sustain the marriage. It is not politically correct to say, but most marriages really do succeed or fail on the wife's desire for them to either succeed or fail. That is not to say that men never mess up their marriages, it is to say that in general wives have far more influence and control over the connection they share.
I emphasize wife, not woman. This dynamic does not hold in dating. An old saying is if you want to test a person's strength, give them adversity. To test their character, give them power. Marriage affords women great power over their husbands, even long after a marriage ends, power they do not have when they are trying to persuade the man to walk down the aisle. How women use this power reveals a great deal about the destiny of the relationship. If their tactic shifts from persuasion to dismissiveness or bullying, the destiny is bleak.