All that was mine in Silvia I give thee. (5.4.5)
Did Valentine just say what we think he said? For a lot of readers and literary critics, this line means that Valentine is offering to "give" Silvia to his friend (who just tried to rape her) as a peace offering that will secure Valentine's friendship with Proteus. Some critics, however, have read the lines a bit differently and argue that Shakespeare is trying to reconcile the tension between male friendship and male-female romance. For these critics, Valentine means to say something like "all the love I feel for Silvia, I give to thee, too." In other words, Valentine could be saying that he will love his friend and girlfriend equally. When it comes down to it, the lines are pretty ambiguous. If we were hoping for Proteus's response to Valentine's offer to clear up the meaning for us, we're out of luck, because Proteus never responds to this line – that's because Julia/Sebastian faints and turns everybody's attention elsewhere.
What is in Silvia's face, but I may spy More fresh in Julia's with a constant eye? (5.4.14)
Here, Proteus reveals that he's fallen back in love with Julia, who is still disguised as "Sebastian." For some readers, Proteus's renewed attraction to Julia raises questions about what it is, exactly, that Proteus is attracted to. He obviously recognizes Julia through the disguise, but it's not clear if Proteus is attracted to her because she looks like Julia, or because she looks like a boy. This moment also reminds us of the fact that the name "Sebastian" is commonly associated with male homoeroticism (as it is in Twelfth Night). Compare this passage to the ending of Twelfth Night, where Duke Orsino proposes to Viola (who is still wearing her "Cesario" disguise).