You’re reading a romance novel or one with a major romantic subplot and then the designated love interest of the female (or male) protagonist does something that hurts the protagonist and you hate them for it, and wish they didn’t end up together… but sure, they end up together.
Due to the nature of this discussion, spoilers from the books are included.
Example of how to write:
Gideon de Villiers from The Ruby Red Trilogy.
>!spoiler here!
Granuailie or however you spell it from the Iron Druid series. She in an unbearable holier than thou backstabbing atrocity of a person that caused the whole series to go downhill and crash and burn in the final book. So much so that I can’t recommend the series to anyone knowing where it is headed, even though up until book 5 I fairly enjoyed it.