Who loved David as himself and made a covenant with him?

Answer: Jonathan

Saul's son Jonathan was knit to David in soul; he loved him as himself and made a covenant with him.

“After David had finished speaking with Saul, the souls of Jonathan and David were knit together, and Jonathan loved him as himself. Then Jonathan made a covenant with David because he loved him as himself.”— 1 Samuel 18:1, 18:3 (BSB)