Damon says that he will take the cure with Elena, however it had already been well established in the show's history that the cure consists of 1 single dose, and cannot be taken by more than one vampire. Both Damon and Elena knew this, yet neither of them brought it up in the conversation.
However, it was established later that when Kathryn had taken the cure that now HER blood was the cure, so Damon could just drink from Elena to be cured.
However, it was established later that when Kathryn had taken the cure that now HER blood was the cure, so Damon could just drink from Elena to be cured.