Romeo and Juliet: Theme Analysis

Love, in its many forms, is an important theme in the play.  The Nurse and Mercutio speak in vulgar terms about love, referring to its physical side.  Romeo's love for Rosaline is simply superficial, childish infatuation.  Paris represents a contractual love.  He does not actually know Juliet, just her family and what she represents.  He is marrying a name, not a person.  Juliet questions Romeo at first as to his intentions, the type of love he has to offer.  The love between Romeo and Juliet is a spiritual, romantic love.  Is Romeo and Juliet's love the superior form? They alone die for their love.
Another important theme is the duality Friar Lawrence speaks of.  Romeo and Juliet are both lovers and enemies.  The Nurse and the Friar both try to help the lovers but ultimately, Romeo and Juliet suffer.  The deaths of Romeo and Juliet themselves are a notable example of this duality.  Their suffering and deaths are tragic however, without them, their families would not have stopped feuding.  Verona was torn by the hatred between the two families.  The sacrifice made by the lovers allows everyone to begin healing old wounds. 
Fate plays an important role in Romeo and Juliet.  Romeo feels that he cannot control the course of his life.  He speaks out to whoever directs [his] sail (I.4) Does fate actually control the course of events or does everyone play a part? If Juliet had not made such a show of obedience, Capulet may not have changed the wedding date.  If there had been more time, Friar John may have managed to get the message to Romeo in time and he would not have killed himself in Juliet's tomb.  If Mercutio hadn't jumped into a fight with Tybalt, he wouldn't have been killed.  He may also have survived if Romeo had not stepped between them.  In either case, Tybalt and Romeo probably wouldn't have fought, Tybalt wouldn't have been killed, and Romeo wouldn't have been banished.  There are several events that could have ended differently if someone had acted in just a slightly different manner or arrived just a moment earlier / later.  Can this be blamed on fate?