English: “And Hashem went.” It was taught: A person should never take leave of his teacher or his friend unless he first obtains permission from him. We learn proper conduct from the Omnipresent, as it is said, “And Hashem went when He had finished speaking to Avraham”—as if to say, “Behold, I am taking leave of you.”
On the daf / in context: The orderly departure of the Divine Presence after the conversation is taken as the model for how a student or friend should take leave.
Type of Learning
Derash on the verse (baraita / Derech Eretz) — not a formal named middah of the 13. Divine behavior teaches human etiquette.
What Is Learned
One should not depart from a teacher or friend without first taking leave; Hashem Himself modeled this by “going” only after finishing the conversation with Avraham.