Callimachus wrote a beautiful poem in circa. 250 B.C. upon learning of the death of his friend, Heraclitus.
You can find the complete and excellent translation by William Cory here, but one line—in particular—gets me every time.
I wept as I remember’d how often you and I had tired the sun with talking and sent him down the sky.
Since discovering this poem in 2014, I have yet to find another description of friendship that has moved me as deeply.
I hope it inspires you today.