How did David and his men respond to the news that Saul and Jonathan had died?

Answer: They tore their clothes and fasted

David and his men tore their clothes, mourned, wept and fasted until evening for Saul, Jonathan, and the people of the LORD.

“Then David took hold of his own clothes and tore them, and all the men who were with him did the same. They mourned and wept and fasted until evening for Saul and his son Jonathan, and for the people of the LORD and the house of Israel, because they had fallen by the sword.”— 2 Samuel 1:11-12 (BSB)