In Romeo and Juliet, how does Shakespeare present characters who are in love?

Perhaps the most well-known love story in history, Romeo and Juliet derives its classic struts from themes that resonate with audiences across time, distance, and culture: much as the love between the title characters transcends the many obstacles they face. Shakespeare's use of language in this play to convey emotion is heightened by the urgency and time span of the lovers' relationship; they fall in love instantly, and are forced to separate because of a feud between their families. This urgency and forbidden quality is seen throughout their dialogue, even when they are talking of other things. 

For example, Romeo scales the orchard walls to observe Juliet on her bedroom balcony, and he compares her to the sun, urging it to rise quicker than nature allows when he says: "Arise, fair sun, and kill the envious moon, that is already sick and pale with grief. Her vestal livery is but sick and green: cast it off!"

Juliet overhears Romeo and says "My ears have not yet drunk a hundred words of they tongue's uttering, yet I know the sound." Again, the emphasis upon urgency and the fast passing of time is emphasized here. 

Shakespeare also uses symbolism related to the cosmos to express the timeless nature of their love, and also to underscore the theme of fate that governs them, the famous "star-cross'd lovers" as the narrator calls them. The cosmological symbols of stars, the sun and the moon are used throughout the play. In the scene described above, there is further reference to the moon when Romeo swears a promise to Juliet by the moon, and she responds: "Swear not by the moon, th'inconstant moon, that monthly changes in her circled orb, lest that thy love prove likewise variable." Here we also see a reference to Romeo's fickle nature, as he had just left a relationship with Rosalind the day before. 

Romeo refers to Juliet with imagery of the sun and the daytime; but Juliet refer to him with the language of the moon and nightfall. Interestingly, in doing so, they also criticize the opposing celestial body. We see this above when Romeo praises Juliet as the "fair sun," and calls the moon "envious" and "sick." Juliet later refers to Romeo with imagery of the night sky when she is waiting for him to arrive ("take him and cut him out in little stars, and he will make the face of heaven so fine, that all the world will be in love with night, and pay no worship to the garish sun." She also says "Come, night. Come, Romeo. Come, thou day in night." ) This is a clever and complex use of language that suggests they are are two separate beings who, when merged together, make a "whole." Also, the oppositional challenges of their love are no match for the strong attraction they feel (and perhaps the source of the idea that "opposites attract").