Don Juan's worst action

In “El Burlador de Sevilla”, Don Juan commits many “immoral” actions but what is his most immoral action? He seduces Isabela under false pretenses, brags about not paying prostitutes, seduces Thisbea, and gets with Aminta. 
I think it stands to reason that the “seduction” of Isabela is far worse than that of Thisbea because Thisbea knows a marriage between them is unlikely, and tricking Isabela ruins her social status far more than Thisbea’s. 
Now let’s compare not paying prostitutes, and his deception of Isabela. Refusing to pay prostitutes breaks the implicit contract between the provider and receiver of a service. On the other hand, Don Juan pretends or at least chooses not to correct Isabela’s misconception that he is someone else to obtain her consent.

Both actions involve obtaining sexual access through deception. In the first, Don Juan misrepresents his willingness to fulfill a financial agreement; in the second, he misrepresents his identity. Both manipulate the other person's understanding of the circumstances under which they agree to sex. If we consider the former a violation because the prostitute would not have agreed to the encounter without the promised payment, we must also recognize that Isabela's consent was premised on an identity that was deliberately falsified. Nevertheless, I consider Don Juan's refusal to pay prostitutes more morally reprehensible because it compounds the sexual exploitation with an additional violation: the deliberate breach of a contractual obligation. He does not merely deceive someone into granting him sexual access; he also exploits an agreement whose fulfillment he never intends to honor. His actions therefore demonstrate a disregard not only for the other person's sexual autonomy but also for the obligations he voluntarily undertakes. Furthermore, there is a distinction in the degree of his deception. In the case of the prostitutes, Don Juan actively misrepresents his intentions regarding payment, deliberately creating an expectation he has no intention of fulfilling. In Isabela's case, at least according to one interpretation of the text, he takes advantage of an existing misconception about his identity rather than necessarily creating it himself. Although knowingly allowing Isabela to maintain that misconception is still deceptive, the distinction between actively manufacturing a false expectation and exploiting an existing one makes the former action worse.