in andrew’s life, there’s a strict system of access. neil made his way into this system not because andrew loves him, but because he went through hell, didn’t betray, accepted the rules, and never questioned them. if andrew says there’s nothing between them, neil silently accepts it and understands that labeling their relationship is pointless. katelyn is an additional variable in his system, representing something from the world of normal people. he sees her as someone who won’t be able to cope with their reality. the desire to get rid of her is a normal reaction for him; that’s exactly how his primitive defense mechanism works.
besides, katelyn is aaron’s attempt to pretend to be normal, but he isn’t. aaron is just as broken as andrew. his girlfriend is a symbol of that “normal life” that andrew hates, because it’s all a lie. andrew knows that in a critical situation, katelyn will either run away or break down, whereas neil won’t. that’s exactly why he trusts neil unconditionally but disregards katelyn. until she proves she’s trustworthy, it’ll stay that way.
the truth is, katelyn doesn’t care about anyone’s approval. her goal is to be with aaron, not to win the blessing of his strange, silent twin brother, who looks at her as if she’s invaded enemy territory and is walking through a minefield. she doesn’t need to prove anything to anyone. it’s enough that aaron chose her.
andrew doesn’t know what she’s really like? she doesn’t care. andrew interpret her unwillingness to prove anything to him as a sign of weakness or indifference? katelyn considers his demands an absurd intrusion into her private life.
they mean nothing to each other, and if he wants to continue treating her like an enemy, so be it. katelyn knows that’s not true, just as she knows that it’s enough for her that aaron will always take her side, just as she will take his.