The question can be answered compellingly either way. The Chorus declares that Romeo and Juliet were "star-cross'd". Romeo refers to "some consequence yet hanging in the stars". After he kills Tybalt, he cries, "O I am Fortune's fool!" One can talk forever about the number of coincidences in the play.
However, the characters' own actions must account tor the tragedy, to a large extent. Romeo, in particular, is very impetuous, and his rash decisions (his quick change of heart about Rosaline, his determination to marry Juliet immediately, and his killing of Tybalt) have terrible consequences.
In the classical sense, there is no such thing as a tragedy of fate. Tragedy is the result of the choices of the characters in the play, the product of their personality flaws. But nowadays we take a more liberal view, and think of "tragedy" as any sad death, regardless of its cause or stature. However you answer this question, you will have plenty of evidence from the text to support your opinion.
I honestly think it was fate. There were too many things that happened to the couple that I do think "the star-crossed lovers" had to be together to matter what. If the servent was literate, Romeo would have stayed home to mope some more. Romeo would have returned to Juliet, banishment or not. It's part of his implusive nature. If it was free will, Juliet would have honored her parents' wish to marry Paris after the party.
As for evidence for this idea of this being a fated love, take a look at how the two describe their love. There are celestial bodies used as metaphors. You have to remember that many Elizabethans believed that all events in life were predetermined by some sort of higher power.
What kind of love did they have? An intense love, one that blasted past most social restrictions on it. Not all restrictions; they still wanted to be married, and they were still concerned with what their families' responses would be.
As far as fate vs. free will, that's a good question. I'd have to say it was fate. There are two reasons I'd say this. The first reason is simplest: in the prologue the chorus refers to them as "star-crossed lovers," suggesting their fate was written in the stars.
The other reason is more philosophical. If you had a choice about who you fell in love with, would you choose an enemy of your family?
Well...... for me the kind of love that romeo and juliet was TRUE love.......they suceded every hindrance and obstacle blocking their way of living happily together.....even if they are the son and daughter of a rival family they still did everything...at the same time it was destined love...destiny also took part in their lives..if mercutio had not persuade romeo to go they wouldnt have met any way... i believe that they are lovers destined to love each other till death do them part....
When dealing with Shakespeare one must understand context. The concept/debate of free will hadn't even been broached yet, and God was in complete control, all things were predestined.
Right in the prologue, the term death-marked as well as star-crossed indicated the presence of fate.
There is other evidence too. Throughout the play Cupid and his arrows are mentioned continually, as if people who fell in love didn't have a choice in the matter. As well, there is some heavy forshadowing with references to death, especially Romeo's last words before he enters the Capulet's party.
Fate is only a word that is used when they don't want to take responsibilities towards their actions. We can either look at it as either "if they would've chose differently..." or we can look at is "that is way it would've gone, whether they had a choice or not".
We make choices everyday, not knowing the outcome. We try to make the best choices, but because of Romeo and Juliet's fatal flaws (desperation, impatience, irration) they did not make the best choices, and ended up dying.
It is of Free will that they ended up dying. Sure, people can argue that is was fate, because of all the coincidences. Such as that they the servant just happened to have them read the guest list, which made them go to the capulet party. But this is just a coincidence, NOT FATE.
It would have been fate if they had chosen the best desicions, and they still died. But instead, they made very rash desicions (Juliet lying to her parents, getting married so quickly, etc) and that's what led them to their death, not fate.
Hope I helped.