I would say it was(show spoiler)
what happened between Eve and Adram. And I hope he dies, not only because of that but because how he treats "his" humans.
Here vampires are ruthless and Eve is intelligent enough to understand that Adram doesn't have a tortured soul/past who just waits for the right woman to save him and turn him into ideal lover. Corbin, it seems, is better (more human friendly) than Adram or others vampires. However there is very little known about him.
Anyway, I'm shipping Eve/Desiree.
I liked reading about Eves's life in the village and her family so I hope we're going to see them in the second book too.