Another interpretation: "For love is as strong as death" (Song of Songs 8:6) — this is the love of Jonathan and David, as it is said, "And the soul of Jonathan was bound up with the soul of David, and Jonathan loved him as his own soul" (I Samuel 18:1). "Jealousy is as harsh as Sheol" (Song of Songs 8:6) — for Saul was jealous of David. And what is love doing beside jealousy?
Jonathan's Love and Saul's Jealousy in Song of Songs
Midrash Tanchuma Buber, Vayeshev 19:2
ד"א כי עזה כמות אהבה, אהבת יונתן ודוד, שנאמר ונפש יונתן נקשרה בנפש דוד ויאהבהו יונתן כנפשו (ש"א יח א), קשה כשאול קנאה, שקינא שאול בדוד, ומה תעשה אהבה בצד קנאה.