Whist I think it's a decent likelihood that Tessa is Saiya's childhood friend, I still don't get how they don't recognise one another. Hopefully not gonna be some half baked ass-pull like the discovery of prosopagnosia, amnesia from head injury, repressed childhood memories, twin shenanigans etc.
.
Also worth noting from comments from the earliest pages that Kip was estimating this story taking ~300 pages. Even if that number isn't accurate, it should indicate that Kip was planning a slow pace from the outset to exhaustively explore certain areas of the story. Either way: strap in, folks.