How does Romeo change from the start of Act I to the end?

Since Romeo has only three days in which to effect any
personality change, little happens within him.  For the most part, he remains
impetuous, emotionally involved with fate--

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Some consequence, yet hanging in the
stars,

Shall bitterly begin his fearful
date...(1.4.13)

and later,
yet feeling the control of fate in his life, he declares, "Then I defy you,
stars!"(5.1.24)--and idealistically in love.  Perhaps the only change in Romeo is the
alteration of his attitude toward the Capulets: While he has hated them as a true
Montague should since the families have long been involved in a vendetta, after having
married Juliet, Romeo softened in his feelings toward the Capulets.  His profession of
love to Tybalt in Act III--

          I do protest I never
injured thee,

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But love thee better than thou canst
devise

Till thou shalt know the reason of my
love.

And so, good Capulet--which name I
tender

As dearly as mine own--be satisfied.
(3.1.68-71)

--attests to
this.

Still, there is some modification in Romeo's
personality. Prior to his secret marriage to Juliet, Romeo was known as a rather
reasonable young man.  But, his reactionary slaying of Tybalt in Act III, along with
his rash murdering of anyone who enters Juliet's tomb indicates that in his desperate
love for Juliet, Romeo lost his reasonableness.  Truly, in Romeo, "The violent delights
have violent ends."