In one meal, Jonathan lost his father and his best friend. It wasn’t that they died, it was the effect of Saul’s behaviour on their relationships.
Saul was so determined to kill David that he mistreated his own son:
1 Samuel 20:33-34 Then Saul hurled his spear at Jonathan, intending to kill him. So at last Jonathan realized that his father was really determined to kill David. Jonathan left the table in fierce anger and refused to eat on that second day of the festival, for he was crushed by his father’s shameful behavior toward David.
Jonathan then had to deliver the news to David, telling him to flee:
1 Samuel 20:41 … Then David bowed three times to Jonathan with his face to the ground. Both of them were in tears as they embraced each other and said good-bye, especially David.