This sentence means that Chunfeng and I can only be regarded as passers-by here, and you are carrying this autumn water and holding the shining Milky Way. It expresses the author's feeling of getting to know someone he likes, but he can't love it. Simply put, I love you, but you love someone else.
Full text:
Chunfeng and I are both passers-by, and you take Qiushui to the Milky Way.
falling into a mundane dream for no reason annoys 3, people.
As a guest in the world of mortals and rain, I hope to have someone to carry an umbrella with me.
mistake old vinegar for ink, and write half your life sour on paper.
I'm more afraid that vinegar and ink will be mixed, and my life will be bitter and sour;
vinegar and ink are accompanied by sugar, and the acidity is more sweet;
bitter memories of life only increase regrets, and laughing at the world of mortals is like clouds and smoke!