This word is called "meet once". The theme reflects the thoughts of friends and bosom friends, and can also be extended to the thoughts of lovers.
The meaning is as follows:
The sound of the piano and the sound of the piano are softly ringing in a low voice. Who can hear my heart?
In the fog, the lyre is still the same lyre, but the bosom friend who played together can't be found anymore. (This can be seen from the allusion "Yu Boya wrestles the piano")
There is no end to regret when you leave. From now on, I just look back and look forward to meeting each other.
In my dream, I am flying with you in the mountains and rivers, and I am willing to exchange my long life with you for a moment.