Philosophical Reviews: Thr Vampyre (Jonathan Polidori)

Jonathan Polidori's Vampyre does not drink the blood of his victims, he is infinitely more diabolical. He is a corrupter of souls. In this case Aubrey is the perfect victim, an altruistic and principled person, who for various reasons is attracted to evil, which does not hesitate to flourish in his soul.

Why did Aubrey not break his promise?

One fact could be the lack of knowledge regarding the consequences of his choices.