This got me thinking about something I don't think I have seen discussed before, RE: life on the ninth house before GtN. The ninth house is a cult, with predictable routines. This is very soothing for Harrow.
Gideon however is an element which cannot be wholly predicted. Its canon that Harrow used Crux as a reality check when she thinks shes hallucinating. How many times did Harrow (upset that she was hallucinating) go to Crux because Gideon re-arranged some skeletons so that they were (sigh) boning, and Harrow thinks its a hallucination at first.
(No one can convince me Gideon didn't do this. Tons of times until it stopped being funny for her, which probably took a while. Gideon had dirty mags and a love of puns and there wasn't much else to do in the Ninth.)
I think that this helps explain a lot of Crux's hate toward Gideon. After all, Harrow is the de-facto head of the religion that Crux has devoted his whole life to serving. He has spent his whole life venerating Harrow and her parents. People bow and scrape when Harrow comes by. The head of his religion comes to him afraid and asking for reality checks because of stupid pranks and such that Gideon would pull, he would hate Gideon for destabilizing Harrow for refusing to conform to the expected routines.
So imagine the stupid pranks left for Harrow to find, the voice Harrow hallucinates (sometimes) being Gideon where she isn't supposed to be according to the routine of the ninth causing Harrow to need more reality checks than she would need without Gideon around, and then muse with me about how
"But I don't even remember about you most of the time."
sounds like Harrow having been reminded she's not hallucinating, its just Gideon, doing what she isn't supposed to again. Think of how that influenced their dynamic, and how fast Harrow shifts how she treats and sees Gideon once they're on the first and there is no routine that Gideon is violating.