2 Samuel 13:20
And Absalom her brother said unto her, Hath Amnon thy brother been with thee? but hold now thy peace, my sister: he is thy brother; regard not this thing. So Tamar remained desolate in her brother Absalom’s house. And Absalom her brother said unto her, Hath Amnon thy brother been with thee? but hold now thy peace, my sister: he is thy brother; regard not this thing. So Tamar remained desolate in her brother Absalom’s house.
Tamar was deeply wronged by Amnon and afterward remained desolate in the house of her brother Absalom. Absalom was her natural protector, and it was in his house that she lived after the wrong. David left Amnon's crime unpunished, offering no justice for what had been done to Tamar. Absalom meanwhile concealed his plan for revenge for two years before having Amnon killed.
Amnon's crime against Tamar and Absalom's revenge in killing Amnon were fruits of David's own wrongdoing. These events kept David mindful of the injustice he had done to Uriah and Bath-sheba.