After Madeline's death, how did Roderick change?

In the days that follow Madeline's death, the Narrator notes the increasing madness of Usher: his skin grows whiter, his ordinary occupations are forgotten, and he roams through the house or stares into space for hours and hours. What frightens the Narrator even more is that he too is beginning to feel "infected" by Usher's condition. The Narrator fears that he too may be going mad.