Multiple times throughout the novel, Orlando's biographer fast forwards through time. These advances in time are usually the result of Orlando sitting down or thinking for long periods of time. Basically, the biographer provides filler for times when he deems Orlando's current action(s) boring. This is especially evident in the passage, with the narrator just listing month after month after month before ending at the same month of the next year. This relates to the themes of time and fact vs fiction prevalent throughout the novel. The amount of time that passes is subjective to the narrator and readers can't be sure whether these advances in time are real (If they are, Orlando would be centuries old by now).

This quote is a metaphor used to indicate the extent of Orsino's anger when Olivia shows up to get Cesario to marry her. What Orsino is basically saying here is, "If I can't have you, no one can," by threatening to kill Cesario (whom Olivia loves) just to spite her. This threat also enhances the fact that Orsino is a self-centered person.