Now Absalom, David’s son, had a beautiful sister, whose name was Tamar. And after a time Amnon, David’s son, loved her. And Amnon was so tormented that he made himself ill because of his sister Tamar, for she was a virgin, and it seemed impossible to Amnon to do anything to her. But Amnon had a friend, whose name was Jonadab, the son of Shimeah, David’s brother. And Jonadab was a very crafty man. And he said to him, “O son of the king, why are you so haggard morning after morning? Will you not tell me?” Amnon said to him, “I love Tamar, my brother Absalom’s sister.” Jonadab said to him, “Lie down on your bed and pretend to be ill. And when your father comes to see you, say to him, ‘Let my sister Tamar come and give me bread to eat, and prepare the food in my sight, that I may see it and eat it from her hand.’” So Amnon lay down and pretended to be ill. And when the king came to see him, Amnon said to the king, “Please let my sister Tamar come and make a couple of cakes in my sight, that I may eat from her hand.” 2 Samuel 13:1-6.
David’s family has some troubling dynamics. He has some uncertain number of wives, who have given him children, and are part of an extended, entitled royal family. Amnon lusts after his half sister, Tamar, for no other reason than that she is beautiful. A friend of Amnon, another loose end in David’s family named Jonadab, concocts a plan for Amnon to get Tamar alone and have her. Amnon is not thinking of the consequences at all, and rapes her. Then he hates her and he throws her out.
This would be bad enough, but Tamar has a big brother who now wants to kill Amnon. This could turn into civil war. And this is all because some royal nitwit thought he was in love when he did not love her at all. He did not care at all what Tamar wanted or how she felt. As soon as he got what he wanted, he was disappointed with her, as if this had been her idea.
David has taken wives and started families that he does not oversee very well. Being a father is a weighty responsibility, and most of David’s sons are willfull and impulsive about romance, like their father.