I never got past the first book of Ilario, so why the head smacking upsideyness?

The character with whom Ilario ends up romantically paired is the obvious choice right from the beginning and, from my perspective, the least interesting of all possible options—presupposing that Ilario had to end up with anybody, which didn't need to happen, either—especially given some of the conclusions Ilario comes to about gender at the end of the book.