In Edgar Allan Poe's "The Black Cat," how did the narrator change over the years?

In s ,
the narrator experiences a descent into madness. The object of his obsession is a black cat
named Pluto, one of his and his wifes many pets.  A previously affectionate relationship between
the narrator and the cat (Pluto . . . was my favorite pet and playmate. I alone fed
him, and he attended me wherever I went about the house) begins to degrade with the
formers alcoholism.  As Poes narrator describes it,

Our friendship lasted, in this manner, for several years, during which my
general temperament and characterthrough the instrumentality of the Fiend Intemperancehad (I
blush to confess it) experienced a radical alteration for the worse. I grew, day by day, more
moody, more irritable, more regardless of the feelings of others.

The narrators psychological state €“ in effect, his transformation
from one-time normal human being with an abiding love of all animals into an alcohol-infused
sadist.

It is in this reduced...