"See how she leans her cheek upon her hand, O that I were a glove upon that hand that I might touch that cheek!"

Romeo is surreptitiously viewing Juliet from a balcony above him in this scene. He extols her tremendous beauty (birds chirping, eyes that would light up heaven, etc.) before remarking on how she is gently stroking her cheek with her hand. His comment: "See how she leans her cheek upon her hand, O that I was a glove upon that hand that I might touch that cheek!" meaning is an indication of his yearning to be a glove, so that he may be the one to touch her cheek (as a glove) (a cheek whose beauty, or "brightness," could shame the stars).

Romeo, like any young lover, is eager to have Juliet to himself. While Romeo just states he wants to touch his lover's cheek in this phrase, we know from earlier moments that he wants to kiss his newfound love on the lips. Romeo was so anxious to be with Juliet that he began kissing her as soon as they met at the Capulets' party! Romeo's impatience and extreme emotional swings, however, are terrible traits that expedite his demise. Juliet, on the other hand, appears to be more in control of her emotions, particularly in this balcony moment. It's almost as if Juliet had to teach Romeo the ways of a "higher love" that goes above simple sexual desires. Despite his evident immaturity, most readers empathize with Romeo's situation.

Romeo - Act 2, Scene 2.