This is an interesting question. The focus on the relationship between the two title characters often creates an image of love that is passionate, unconditional, and at times even destined. However, the intensity of their bond ostensibly obscures any notions of love within the play that are based in realistic thinking. If you look at how love is treated in other relationships in the play, you might see a subversive and even facetious commentary on the nature of Romeo and Juliet's relationship.
For example, consider the "love" that Romeo has for Rosaline. Romeo's group of friends often mock him for being something of a "bleeding heart" or "loverboy." Indeed, while his love is passionate, it is implied that it lacks any basis in a mental attraction or interest in Rosaline as a person. Romeo is possessed by infatuation rather than love in this situation. That is to say, he is far more in love with the idea of Rosaline than with Rosaline herself. How quickly he shifts his obsession from Rosaline to Juliet is evidence enough for this point.
Juliet's position and eagerness to be loved unconditionally likely also stems from a dysfunctional "love" in the characters around her. Lord and Lady Capulet agree on virtually nothing, favoring different children (Tybalt in the case of Lady Capulet) and fixating on completely different methods of raising Juliet. Lady Capulet takes on a diminutive role. Her relationship with Lord Capulet is implied at times to be abusive. However, she will always "stay in her place" because, ultimately, Lord and Lady Capulet are more concerned with their social rank and outward appearances than with being a functioning, healthy family. It is perhaps this dysfunction that leads Juliet to yearn for a "true" love.