In the second half of the twentieth century, the popular songs were all about love. From "She loves you, yeah, yeah, yeah," to "Paint it black," to "Leader of the pack," they were about falling in love, being in love, losing one's love. In spite of some modern rap songs about going out and shooting people, love still dominates the airways.
This focus on love seems so normal that it may be hard to realize how unusual it is. But in fact the twelfth century and the twentieth century have been the predominant times in the West when love dominated popular culture.
Vernacular literature, that is stories written in the everyday language rather than in learned Latin, had its start at the beginning of the twelfth century with the epic "Song of Roland." But this epic, in which the only appearance of love is when (spoiler alert!) Roland's fiancée faints and dies after hearing of his death, was quickly joined by romances, in which falling in love drove the plot.
The romances both glorified and critiqued love--never following any set "code" such as one might now mistakenly call "courtly love." King Arthur stories were a creation of the twelfth century, and love dominated these stories, but very often it was forbidden, adulterous love. Both the love between Lancelot and Queen Guinevere, and the stories of the love between Tristan and Isolde which inspired the Lancelot stories, are descriptions of sin. The characters, the authors, and the audience all knew this. It could be fun, but you were going to hell.
In twelfth-century epics (after "Roland") and romances, the women were all very active participants. In some cases they led men astray, but more often they saved the day. In "Guillaume de Dole," the heroine personally pleads her case in court and ends up tricking the man who untruthfully boasted that he had had an affair with her into confessing. In the epic "Raoul de Cambrai," even though most of the men end up killing each other, it is clear that their problem was that they did not listen to the women.
The romances that glorified love suggested that it was a reason to get married. Now it had always been assumed that husbands and wives should love each other and be true to each other (see more here on medieval marriage and medieval sex), but for the first time in the twelfth century falling in love came first, as a reason to get married rather than something that came after the wedding.
In practice, no aristocratic parent was going to allow their teenage children to wander around the countryside, find an appropriate partner, fall in love, and then get married. Marriage alliances were too important to allow that kind of randomness. But that is what happened to the heroes and heroines of medieval romance. Interestingly, they generally fell for someone who it was right that they should marry anyway.
Twelfth-century courts, where unmarried men and women mingled, must have been full of meaningful glances, stolen kisses, passed notes, and broken hearts. The romances described the symptoms of falling in love as fevers and burning aches. The adults appear to have tolerated such behavior as long as everything stayed platonic--and a medieval castle would have had very few opportunities for privacy.