What does the long confession tunnel mean?

The long tunnel of confession is a joke told by beginning of winter. The saddest thing is not that you didn't sleep with that girl. The saddest thing is that after many years, you forget whether you slept with that girl or not. It was in the tunnel that beginning of winter wanted to tell a joke. Later, when beginning of winter asked what was the name of Achuan Tunnel, Achuan said there was no tunnel near here. Beginning of winter told the joke twice, and the joke about the tunnel was forgotten. In the memory of Liuchuan and beginning of spring, the tunnel doesn't even exist.