William Shakespeare's tragedies are rife with this trope... Tybalt and Romeo? Check. Cassius and Caesar? Check. Iago and Othello? Check. Coriolanus and Aufidius? Check. Antonio/Shylock? Check. And in this case, people with fancy degrees actually spend too much of their time researching and writing about it.
The comedies aren't free, either. Valentine/Proteus, anyone?
Nor are the histories, which give us Hal/Hotspur and Richard III/Bolingbroke.
Tybalt and Romeo? How about Romeo and Mercutio?!?
Jean Valjean and the original Inspector Javert from Les MisÚrables. Hey, the woman whose child you've sworn to raise as your own has just died from an STD? No problem — just sing a song with your sworn nemesis!
Let the record show that the song in question named "The confronation" Is about how Valjean is vowing to go and save the child immediately, and Javerts desire to stop him, leading to Valjean even claiming he will kill Javert if he has to.