The Chorus in the Prologue of Act II offers us a summary of what has happened in Act I and where things lie concerning the two lovers of the title of this excellent tragedy. The first four lines indicate what has happened to Romeo and his love for the "fair Rosaline":
Now old desire doth in his deathbed lie,
And young affection gapes to be his heir;
That fair for which love groaned for and would die,
With tender Juliet matched, is now not fair.
Note the way in which a metaphor is used to compare Romeo's former love for Rosaline to an old man on his deathbed, with his new love for Juliet being compared to the old man's heir, waiting eagerly for his relative to die so that he can inherit all. Romeo's love for Rosaline, which caused him to "groan" and say that he would die for her, is now surpassed by his new love for Juliet. Comparing Juliet and Rosaline, Rosaline "is now not fair" as Romeo forgets Rosaline and moves away towards his new love with Juliet.