How does the playwright gradually develop Tom's character throughout The Glass Menagerie?

The opening of the play begins with Tom's narration.  We
are introduced to him as our guide through the Wingfields and their intense emotional
states.  This means that we see Tom after the action he narrates or through which he
guides us has passed.  At the same time, Williams reveals Tom to be a character that is
not entirely happy with his life, the one we see after the drama has taken
place:

I am
the narrator of the play, and also a character in it. The other characters are my
mother, Amanda, my sister, Laura, and a gentleman caller who appears in the final
scenes. He is the most realistic character in the play, being an emissary from a world
of reality that we were somehow set apart from. But since I have a poet’s weakness for
symbols, I am using this character also as a symbol; he is the long delayed but always
expected something that we live
for.

Consider a couple of
elements we see about Tom right from the first scene.  The idea that the family is "set
apart" from reality is one level of understanding that Tom gives.  Seeing that he is now
apart from this level, it is another distance from which Tom speaks.  At the same time,
Tom's "poet's weakness" helps us see a predilection for melancholy, something that is
reemphasized throughout the drama and indicative to us that Tom is not entirely happy
with everything in the drama and that which followed
it.

Over the course of the play, Williams brings out Tom's
fundamental conflict with Amanda.This is a chasm that widens over the course of the
drama.  Williams makes it clear that Tom's hatred of his mother exists almost in the
same magnitude as his loyalty towards his sister and his desire to not be like his
father.  This is how we first see Tom.  As the drama unfolds, it becomes apparent that
the wedge of disdain grows in intensity and power, superseding the bonds of loyalty and
the fear of repeating the past.  Williams constructs Tom to be increasingly resentful of
Amanda and as the play progresses, with her fears increasing, Tom recognizes that he can
no longer endure being with his family.  As the play reaches its end, Williams has Tom
leave.  This is what makes the development of Tom so intensely powerful.  On one hand,
he has left the family that was the source of so much self- hatred.  Williams has given
Tom independence.  Yet, Williams was wise enough to make the argument that freedom and
independence do not automatically guarantee happiness.  In the end, we have to come back
to Tom at the start of the play.  The melancholy we see within him at the start of the
drama concludes Williams' development of him as one who possesses freedom and
independence and cannot seem to find happiness because of it.