I am not musical but if I were I'd be writing one very sad song now about someone who seems to have, in modern parlance, "moved on" from a friendship we once shared.
I did, however, find one small snippet of prose which says it all. It's from Ralph Waldo Emerson's Essay on Friendship.
I awoke this morning with devout thanksgiving for my friends, the old and the new. Shall I not call God the Beautiful, who daily showeth himself so to me in his gifts? I chide society, I embrace solitude, and yet I am not so ungrateful as not to see the wise, the lovely, and the noble-minded, as from time to time they pass my gate. Who hears me, who understands me, becomes mine, — a possession for all time.
Nor is nature so poor but she gives me this joy several times, and thus we weave social threads of our own, a new web of relations; and, as many thoughts in succession substantiate themselves, we shall by and by stand in a new world of our own creation, and no longer strangers and pilgrims in a traditionary globe. My friends have come to me unsought. The great God gave them to me.