Who says he didn't? I'm sure they didn't only do it once, why not in both forms at different times?
The novel itself makes it pretty clear that the guys get very...animalistic. I dont think a single ones of the times they're together, the guys human. She seems cool with it though and prefers joining with Curtis. Parker is very energetic and rough. Curtis is more slow and sensual.
omg! There's a novel?!Please link
I tried reading it, but it's not that good in my opinion. It feel like a badly written fanfic of the manga and is hard to follow what's happening at times, so I dropped it.
I really want curtis to make with Bai in whole human form, not hapf snake. Like how humans make love amd please less sensore if possible (▰˘◡˘▰)