here are several possible sources for The Two Gentlemen of Verona. The most important text upon which Shakespeare relied is the Spanish pastoral romance called Diana Enamorada, written by Jorge de Montemayor and published in 1542. Shakespeare would have had access to one or more of the many English translations of this text before 1598. Shakespeare owes the main plot of his play to Diana Enamorada, and there are many small similarities between the lovers in The Two Gentlemen of Verona and the lovers in his source. Karl Young, in his Yale edition of the play (1924), summarizes these similarities:
Among the chief matters in which the play resembles the narrative are the following: Proteus’ employing Julia’s maid as intermediary, and Julia’s exhibition of coyness in receiving his letter (I.ii); the breach in the intimacy of the lover caused by the sending of Proteus to court; the pursuit of Proteus by Julia in disguise; Julia’s lodging at an inn and overhearing Proteus’ serenade to Silvia (IV.ii); the disguised Julia’s taking service with Proteus as his page, and being sent by him to advance his suit to Silvia; the conversation between Julia and Silvia concerning Proteus’ former love, and Silvia’s rejection of his addresses (IV.iv); and Julia’s final reunion with Proteus in the forest. (90-1)
A second source seems to be the story of Titus and Gisippus, a tale found in Boccaccio’s Decameron, written in 1353. Proteus’ soliloquy in Act II, Scene VI of the play resembles closely the lines spoken by Titus in Boccaccio’s work. Another minor source was Arthur Brooke’s The Tragical Historie of Romeus and Juliet, which he also used as the basis for his tragedy Romeo and Juliet. From Brooke’s text Shakespeare adopted the monk, Friar Laurence (see Act V, Scene II, 35-48), and Valentine’s ladder. Very generally, Shakespeare was likely inspired by the work of John Lyly and poet-musician Richard Edwards, who wrote the rhymed play Damon and Pithias, which was acted in 1564 and printed in 1571.