They're paired; they were actually supposed to be the same story but there's a third scene in the middle that I didn't feel like writing so instead we have a G-rated pre-slash thing (which can be read as nonslash if you feel like it) and then a NSFW slashy sequel in which there is sexing.
Eboli's Gift, rated G
Olive Oil and Orange Trees, rated explicit omg.
The opera is Verdi's Don Carlo (or Schiller's play Don Carlos, Infante of Spain), only partway through the first story I deviate from canon into an AU where Posa doesn't die.