What does it mean that leaves wither and are no longer green, and people wither and go with the flow?
It means that the leaves are not as green as before, and people lose their judgment.
I used to be a deep ocean, and I had deep feelings, but in the end, I was washed away by the ups and downs of the world like a dead leaf, fell into the river of time, lost my personality, lost my position and lost the ups and downs of the world.