What are some quotes from Romeo and Juliet showing their dependence on one another?
Romeo and Juliet become codependent almost immediately in Romeo and Juliet, and this is one of the reasons their relationship becomes so hurried and ultimately deadly. (Although I do not think Shakespeare intended Romeo and Juliet to be read as a play warning of the dangers of codependency, it can certainly be read with that framework in mind.) Here are two quotes that point to the dependency Romeo and Juliet share:
ROMEO: Arise, fair sun, and kill the envious moon, / Who is already sick and pale with grief / That thou her maid art far more fair than she. Be not her maid, since she is envious; / Her vestal livery is but sick and green, / And none but fools do wear it; cast it off. (II.ii.3-9)
Immediately, Romeo compares Juliet to being more beautiful than celestial bodies like the moon. This is a big claim and indicative of his uncontrollable feelings for Juliet.
JULIET: Come, gentle night; come, loving, black-browed night; / Give me my Romeo; and, when he shall die, / 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. (III.ii.20-25)
Whether Juliet's feelings can be classified as lust, love, or a crush, it is clear that she is consumed by her thoughts of Romeo. In her public moments she figures out how to be with him, and in her private moments she can only think of him. This is similar to many young, dependent relationships.
Interestingly, it's important to note that the dependency between Romeo and Juliet is often expressed through celestial imagery. Shakespeare is stating that Romeo and Juliet circle each other in the same way that planets and moons orbit each other, tied by gravity.