Perhaps it was not until the moment of death that Mu Ran dared to say the words he wanted to say the most: "Cheng Ming, I miss you very much."
As for Cheng Ming, he had been burdened with too many things early on. In order to protect his lover, he had no choice but to disappear from Mu Ran's world.
In the end, Cheng Mu's ending is that they both die in old age and never see each other again, or is life saying that it is rare to be free and unrestrained?