Amnon and Tamar

In the course of time, Amnon son of David fell in love with Tamar, the beautiful sister of Absalom son of David. (II Samuel 13:1)
Tamar also was Amnon's sister by a different mother. David had several wives. Apparently Tamar was King David's only daughter.
Notice the expression, "fell in love."
There is a difference between "love" and "glandular appetite," and it is this difference that is the subject of the present essay.
There are many kinds of love: mother for son, a human for an animal, a couple who are preparing for marriage. Love is self-sacrificing. In the case of marriage, the one holds the other of more importance than himself or herself.
Glandular appetite is a physical desire. It is not at all self-sacrificing. Its motive is to please itself, to make itself feel good. Its purpose is to reproduce the parents so that God has a population from which to draw His Kingdom.
It appears from history that once a nation of people arrive at an acceptable standard of living, their attention turns to sexual activity. Before long various sorts of sexual activity begin to occur, all kinds of perversity, until finally God removes that nation from its place of prominence and seeks another people who are more disciplined.
So genuine love and sexual activity have little in common. Sexual activity ordinarily is not intent on bringing peace and joy to the partner but to experience a physical thrill. It is entirely self-centered, although it may accompany the genuine love of marriage.