[Graham]

Very readable, with nicely paced twists which I didn’t see coming. The revalations worked for me:

Spoiler:

I understood how the first night effect of the Itch worked as written, so if you are tweaking to support arjaybe's comments, I don't think it needs to be by much.

The only thing that I did wonder was whether Gavin needed to come across as such a jerk in the opening few paragraphs.

Spoiler:

I can’t make my mind up whether having Gavin being so unpleasant for the first few paragraphs is necessary for the plot to work or whether the potential for turning some readers off the story early might be worth toning it down a little.

I think you're down to the line editing on this one; the structure and feel are good. Do you want to do another pass before we weigh in too heavily on line edit comments or would these be helpful now?

Graham