2.5 stars. I'm really, really disappointed. When I see Kasie West's name on a book cover, I have expectations, and The Fill-in Boyfriend managed to not meet them on just about every level. 
 One thing that can really make or break a novel is the development of secondary characters. The supporting cast of FIB--with the sole exception of Bec--broke this book. Bec was a well-rounded character with her own arc independent of the book. Gia's parents were uninvolved robots, her brother Drew is a selfish asshole whose sole existence was to push an underdeveloped plot point about social media that I'm sure most would pinpoint as the cause of Gia's growth (I don't), and her ex-boyfriend is a cardboard cutout with muscles. He has like five lines and zero personality. Laney is equally unimportant, despite being one of Gia's best friends. Claire gets ALL the attention, and while I respect that she was hurt, she lets herself be manipulated and never shows signs of true friendship toward Gia. Jules is a caricature of Regina George for NO EFFING REASON AT ALL. I'm sure all that nonsense about her mom is supposed to make me sorry for her, but she is stereotypically mean in a way that prevents any other sort of development. She's flat, with no depth or complexity. It works in Mean Girls because that's a satire. It doesn't work here. And then Hayden's own friends are equally useless and horrible, with Spencer basically playing the role of that douche Ansen feom Easy A. The overall effect is a pitifully weak supporting cast that dragged the story down every page, every paragraph, every sentence that wasn't solely about Gia, Hayden, or Bec. 
 Fyi, I think Gia was working on being a better person before Drew's special little video. I appreciated the growth she exhibited throughtout the novel. I did not appreciate Drew's complete lack of awareness or lack of understanding irony when he posted a video against social media addiction ON A SOCIAL MEDIA SITE. What a tool. And not being aware of the fact that he was friends with his sister's friends on Facebook? IDIOT. 
 As for Jules, because I don't think I've abused her enough, I actually can't write in a review all the words I'm calling her in her head. Speakig of Easy A, the one Emma Stone calls that one chick during English class? That's one of them. Jules is a plot device, not a character. She exists to cause conflict, but it's not nuanced, interesting conflict. She abuses Gia's trust, lies to everyone's face (and has the balls to Gia a liar in the same breath), manipulates her friends, and is all around terrible. The worst thing is, I do feel sorry for her. Not sorry for Jules because of her family, but for the fact that she was never developed past this horrible cliche. I almost could have stomached it if there had been a grand twist that revealed her motives, but nope, she was mean for mean's sake. Blech. And because of Jules, the conflict with Gia's friends is never truly resolved, which makes the book feel unfinished and me feeling unsatisfied. 
 Reasons why this book wasn't a total bust? Kasie can write the CRAP out of romance. She gives good tension, and Gia and Hayden were overflowing with yummy chemistry goodness. I do think just their relationship would not have made a book by itself, but the other plots were so tired and boring that I resented them. Gia had a very real and understand trajectory of growth. I like that. She's a bit shallow at the beginning, which I'll always allow, and she developed into a more dynamic character. Hayden was fairly perfect in typical ya boy fashion, but he also had depth and complexity. I liked that he was an actor and could be the suave confident boy, but his mask always slipped just a bit so you could see the real Hayden just underneath. And he messed up. Messed up BIG. But he knew it and took his lumps. 
 The real star of the show, though, was Bec. She's intriguing. Why does she try on so many different images? I'm dying to get in her head and discover the back story there. Bec also showed real growth and maturation, which makes me sad for all the side characters who didn't get that opportunity. She's sassy, she's wise, she's genuine. Give me a Bec book, and maybe I'll forgive the jumbled up frustrating mess that was The Fill-In Boyfriend.