Jonathan loved David like he loved himself! Amazing when you think that to Jonathan, David being the next king was as good as himself being the next king. And we all are likewise called to love others like we love ourselves.
https://vision.org.au/the-word-for-today-reading/
Pretty well my favourite Bible story.
It speaks to the overreaching qualities of both men, in this particular instance they set an incredible behavioural standard.
I love the love that is shared between Jonathan and David and if I’m honest, I’m quite envious of deep connection like that. 
Discussion
This also shows that Jonathan loved God and God's will above himself and his own desires. He respected that God had chosen David, and not himself, to succeed his father Saul to the throne, and he was content with that and supported David.