I'm really starting to hate this girl. MC really deserves someone better.
Generally speaking, stories of this sort are written to appeal to an audience who see themselves as like the FMC.
More generally, if the central character in a work of fiction is a jerk, then usually the author imagines the audience as a bunch of jerks, or is him- or herself a jerk seeking vindication, or both.
And most of the people who stick it out in stories about jerks are indeed jerks, which is why, when someone calls the principal character a jerk in the comments, a wave of counter-attacks usually follows.