Complex sentence: Genji is aware of the affair over by his wife and nephew Kashiwagi, however does not crush him, instead feeling that perhaps this is karma for Genji himself committing adultery with his step-mother Fujitsubo.
Split into simpler sentences: Genji is aware of the affair by his wife and nephew Kashiwagi. However, this does not crush him because he feels that perhaps this is karma, for Genji himself is committing adultery with his step-mother Fujitsubo.