The truth was they knew their love was wrong, forbidden and twisted, but it had saved them through there younger years with their years of abuse. This love had carried into later life despite going their own ways. There was always a connection there, but Narcissa knew she had to cut off the emotions and feelings towards her own blood. She never truly wanted to. Bellatrix was her only true home. She knew she had to in order to protect her son from the pain of losing his father. A protective mother who had never truly had enough leverage to leave the monster that caused their grief.