>>725680392 (OP)
Andrew is "corruption" almost perfectly embodied in a man. His natural intelligence and ability to understand others could have been virtuous traits, but his mother placing the heavy shackle of "taking care of your sister" onto him, and almost entirely him alone because she's an absentee uptight bitch is what begins to warp him.
From the very beginning, a large part of his active psychology is dedicated to Ashley. Because of her rampant psychotic behavior and lack of responsibility for her actions, this all gets shoved onto Andrew, as her caretaker. He becomes used to her patterns, and the most fatal flaw is Ashley herself.
Ashley is smart enough to see what she's doing to Andrew. She constantly manipulates him throughout their lives, and whether consciously or not, it ends up shifting his psychology away from "keeping Ashley safe" to "keeping Ashley free from consequences". We see this in the grandparent's house most strongly, where Andrew allows Ashley to erase his work in the garden. This moment solidifies his lack of control over her, and her subconscious control over him.
We see Ashley having nightmares about "losing control" over Andrew and having him act on his latent hostility for Ashley ruling his emotions and life, and these are real concerns. Andrew kills in the story, cold blooded, and is able to compartmentalize it, because not doing so would have compromised Ashley's safety. He went from a promising young boy, to a runaway murderer that only cares about his sister, because of their close bond, shitty parents, and her terrible pathology.
In summary, corrupted intelligent murderous boy that can still feel shame and anger = hot
