Dear Book 3, What the fuck?

Dear modern guilty pleasure YA books, why does the third book always suck? Seriously. What the fuck is up with that?
Okay, so first of all a brief summary. Chloe is a "typical" (we'll come back to this) teenager who finds out her biological mother and she herself is a cat person known as the Mai. Tada! Told you it would be brief.
So, while book 1 and 2 were full of entertainment value. I had to regularly pretend that Chloe was 18 or 20. There was just waaaaay too much sex for me to be comfortable reading it in a "she's 16," sort of way. It was sort of pedophiliac in a few scenes, the one outside a club still makes me cringe just thinking about it. I know 16 year olds have a lot of hormones and most of them (so it seems) are not virgins, but goddamn, I don't need to read about it in graphic detail. I'm 27 - it made me uncomfortable and I'm regularly a horny fuck. I'm no prude, I swear. Sex is part of life, and therefore should be a part of literature, but goddamn, this just made me squirm and not in a fun way.
And the third book. Can we just say anti-climactic? It built and built and built and built until it broke ... and then it just ended.