Why is the narrator attracted to the rich widow at the Club? Why does he feel responsible for her death?

He likes the fact that she is really white and cultured. She was everything he felt he was pretending to be. He was angry because she was with a visibly black fellow,

"This woman was known at the “Club” as the rich widow. She -went by a very aristocratic sounding name, which corresponded to her appearance. I shall never forget how hard it was for me to get over my feelings of surprise, perhaps more than surprise, at seeing her with her black companion; somehow I never exactly enjoyed the sight. I have devoted so much time to this pair, the “widow” and her companion, because it was through them that another decided turn was brought about in my life."

Oh the black chap she was with eventually shoots her when he thinks she is flirting or having a "thing" with the narrator.