Were 't not affection chains thy tender days To the sweet glances of thy honour'd love, I rather would entreat thy company To see the wonders of the world abroad (1.1.3-6)
Valentine wishes that his best friend would join him to "see the wonders of the world abroad," but Proteus's love for Julia prevents his friend from leaving Verona.
VALENTINE To be in love, where scorn is bought with groans, Coy looks with heart-sore sighs, one fading moment's mirth With twenty watchful, weary, tedious nights: If haply won, perhaps a hapless gain; If lost, why then a grievous labor won; However, but a folly bought with wit, Or else a wit by folly vanquishèd. (1.1.30-37)
At the beginning of the play, Valentine is cynical about love. If a man succeeds in winning a woman's heart, he says, it is a "hapless gain." On the other hand, if a man loses in love, it's a "labour won."
PROTEUS I leave myself, my friends and all, for love. Thou, Julia, thou hast metamorphosed me, Made me neglect my studies, lose my time, War with good counsel, set the world at nought; Made wit with musing weak, heart sick with thought. (1.1.67-71)
Proteus declares that his love for Julia has transformed him. Ever since he fell in love with Julia, Proteus doesn't study, he argues with his friends, and isn't very witty. Understood this way, love does not change one for the better.
This passage seems to anticipate what famous essayist Francis Bacon later writes (c. 1600) about male-female love: "You may observe, that amongst all the great and worthy persons (whereof the memory remaineth, either ancient or recent) there is not one, that hath been transported to the mad degree of love: which shows that great spirits, and great business, do keep out this weak passion" (Francis Bacon, "Of Love").
JULIA His little speaking shows his love but small. LUCETTA Fire that's closest kept burns most of all. JULIA They do not love that do not show their love. LUCETTA O, they love least that let men know their love. (1.2.29-32)
Julia thinks that a man's love can be measured by the words he speaks, as if love is somehow quantifiable. This sort of reminds us of King Lear, who famously asks his daughters, "Which of you shall we say doth love us most?" (King Lear, 1.1.2).
PROTEUS Sweet love, sweet lines, sweet life! Here is her hand, the agent of her heart; Here is her oath for love, her honor's pawn. O, that our fathers would applaud our loves To seal our happiness with their consents. O heavenly Julia! (1.3.46-51)
Proteus is madly in love with Julia and wishes that their dads would get on board with their relationship. In the play (and in Shakespeare's time), young couples typically married only after their fathers' gave permission.
SPEED Marry, by these special marks: first, you have learned, like Sir Proteus, to wreathe your arms, like a malecontent; to relish a love-song, like a robin redbreast; to walk alone, like one that had the pestilence; to sigh, like a school-boy that had lost his ABC; to weep, like a young wench that had buried her grandam; to fast, like one that takes diet; to watch like one that fears robbing; to speak puling, like a beggar at Hallowmas. You were wont, when you laughed, to crow like a cock; when you walked, to walk like one of the lions. When you fasted, it was presently after dinner; when you looked sadly, it was for want of money: and now you are metamorphosed with a mistress, that, when I look on you, I can hardly think you my master. (2.1.18-32)
When Valentine travels to Milan, he falls in love with Silvia. (So much for the cynical Valentine we saw in Act 1, Scene 1.) Here, Speed mocks him for having been "metamorphosed" by love and suggests that Valentine has changed so much that he's hardly recognizable.
SILVIA Nay, then, he should be blind, and being blind How could he see his way to seek out you? (2.4.93-94)
Silvia raises an excellent question. If Proteus loves Julia so much, why is he leaving her in Verona and travelling to Milan, where his best friend Valentine is hanging out? The easy answer is that Proteus's dad is making him. Still, Silvia's shrewd question seems to gesture at the fact that Proteus isn't as dedicated to Julia as he claims to be.
PROTEUS Methinks my zeal to Valentine is cold, And that I love him not as I was wont. O, but I love his lady too too much, And that's the reason I love him so little. How shall I dote on her with more advice That thus without advice begin to love her? (2.4.213-218)
For Proteus, falling out of love with Julia means that his "zeal" to Valentine is "cold." In the play, it seems like a man's romantic interests always threaten to break up his friendships with other men. It's also pretty clear that Proteus is fickle – he easily falls in and out of love.
JULIA Then let me go and hinder not my course I'll be as patient as a gentle stream And make a pastime of each weary step Till the last step have brought me to my love, And there I'll rest, as after much turmoil A blessèd soul doth in Elysium. (2.7.33-38)
Although Proteus falls out of love with Julia as easy as we might change a pair of socks, Julia's devotion to Proteus is pretty rock steady – she willing to risk everything to follow Proteus to Milan so the couple can be together. Here, she declares that her reunion with Proteus will be just like heaven.
VALENTINE And why not death rather than living torment? To die is to be banished from myself, And Silvia is myself; banished from her Is self from self—a deadly banishment. What light is light, if Silvia be not seen? What joy is joy, if Silvia be not by—
Unless it be to think that she is by And feed upon the shadow of perfection? Except I be by Silvia in the night, There is no music in the nightingale. Unless I look on Silvia in the day, There is no day for me to look upon. She is my essence, and I leave to be, If I be not by her fair influence Fostered, illumined, cherished, kept alive. I fly not death, to fly his deadly doom; Tarry I here, I but attend on death, but, fly I hence, I fly away from life. (3.1.174-191)
This is one of the most famous speeches in the play. Here, Valentine laments that he's been banished from Milan and his beloved Silvia. In elevated terms, he declares that life is meaningless for him without her, so much so that fleeing from Milan is the same as "fly[ing] away from life." This reminds of the character "Juliet," who says that Romeo's banishment is like a death sentence (Romeo and Juliet, 3.2.10).
VALENTINE All that was mine in Silvia I give thee. (5.4.89)
After Proteus apologizes to Valentine for trying to steal his girlfriend, Valentine immediately forgives him and makes a peace offering. There seems to be a few ways to read this passage:
Any claims I made to Silvia's love, I give thee. (He's going to step aside and let Proteus have her.
All the love I gave to Silvia, I give thee. (Valentine loves Proteus more than he loves Silvia.
All the love I gave to Silvia, I'll give to you too. (He'll love Proteus and Silvia equally.)
Either way, things aren't looking too good for Silvia, who was nearly raped by Proteus and is about to get formally engaged to a guy who doesn't place her first.