In the end, what does Tom realize about his dreams and how does he come to this realization?

In Tennessee Williams's Expressionistic drama,
The Glass Menagerie,Tom, as narrator and character in the play, realizes that
his passionate search for meaning in his life by using his art of poetry to ease his
pain has been delusionary.  For, he is yet alienated and emotionally overwhelmed by the
memory of Laura that he cannot escape:

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I pass the lighted window of a shop where
perfume is sold.  The window is filled with peices of colored glass, tiny transparent
bottles in delicate colors, like bits of a shattered rainbow.  Then all at once my
sister touches my shoulder.  I turn around and look into her eyes...O Laura, Laura, I
tried to leave you behind me, but I am more faithful than I intended to
be!

The symbolic imagery of
the dimmer light of candles points to the extinguishing of Laura's hope and both Tom and
Laura's dreams in the desperate 1930s of the setting. When Tom tells his sister "Blow
out your candles, Laura," he extinguishes both hers and his search for meaning in life. 
This use of expressionistic techniques reflects the hopelessness of Tom's emotional
sensibilities.