Well since no one has addressed it in this thread yet [I'm guessing its more like a unspoken thing between the writer and the reader?] Here was what I took from the last 20 chapters, I'll try to be as spoiler-less as possible for those who are too curious but have yet to read this masterpiece. Honestly, it is by pure stroke of luck that Fakku of all places got to witness this firsthand.
My answer to the last mystery of the story
So a bit after the sex scene with the jacob imposter, the lead mentioned something about understanding if the jacob she was with was actually the horse because whoever she is with at that exact moment is the one she loves regardless. I take it from that that she was willing to drop the real jacob for the horse jacob. Which lead me to question exactly how faithful the lead in the story really is. Could she also be one of the benefactors behind having the others trapped in that cellar/eternal rape dimension? There were quite a few hints in the entire book [even if you don't count the whole jacob subplot] that point to the lead actually being the badguy instead of the one the reader is suppose to be sorry for. Sure she was in the cellar with the rest of them but make note that the author RARELY focuses on what is going on with her almost to the point that it appears that the lead had either figured a way to escape with the necklace/sword thing that was given to her [remember she hid it as a sex toy in chapter 32 to avoid inspection], or actually disguised herself as one of the eternal sex fiends. In short, I think that the sex fiends and the lead made a deal to get them more bodies for their hunger and that the lead truly does not feel bad that she was the cause of her mothers own death because of it.