Romeo's speech in Act 1, scene 1 comes after the fight in the streets amongst the servants of the two houses, and the Prince's warning to both of the consequences of public violence. Romeo's response is a series of oxymorons:
Why then, O brawling love! O loving hate!
O any thing, of nothing first create!(175)
O heavy lightness! serious vanity!
Misshapen chaos of well-seeming forms!
Feather of lead, bright smoke, cold fire, sick health!
Still-waking sleep, that is not what it is!
Thus, in Romeo's mind (and throughout the rest of the play), the concepts of love and death are inextricably connected. His diction reflects the strife of civil violence that the two families will propagate. However, it also reflects his own suffering under his "love" for Rosaline. This is not a mature emotion toward another though; it is a teenager's infatuation, superficial and obsessive. He is moody, melancholy, and generally depressed.
In the next act, Romeo’s character has developed from a shallow infatuation for Rosaline to a more mature romantic love for Juliet. Romeo’s soliloquy in Act 2, scene 2 conveys an idealized quality of their love and clearly describes his new feelings for Juliet in terms of brightness. He even states that the brightness of her eyes, if up in heaven, would light up the skies and make the birds think it was day. He again uses imagery of light and dark when he first sees Juliet on the balcony and states,
But soft! What light through yonder window breaks?
It is the East, and Juliet is the sun!
Arise, fair sun, and kill the envious moon,
Who is already sick and pale with grief(5)
That thou her maid art far more fair than she.
Be not her maid, since she is envious.
As Rosaline was compared to moon and night, Juliet is compared to sun, brightness, warmth, and light. Even the sense of heaviness and weight that Romeo associated with Rosaline have transformed to a weightlessness, an ability to fly over walls (which is how Romeo claims to have gotten into the orchard in the first place).