Whoa. It's been almost a month already? Time flies when you're having fun… or being held hostage by your ex-high school boyfriend. Desi won't let Amy leave and is basically smothering her with his presence. He has to know where she is in the house at all times, and he even suggests moving in with her so he can better protect her from whatever she needs protected from (or better make sure she doesn't leave).
Fortunately, Desi probably won't move in because that would require explaining Amy's presence to his mother, who hates Amy. We learn here that back in high school, Amy scratched up her own face and told Desi his mom attacked her.
Since living at Desi's place, Amy's lost weight and colored her hair back to its original shade because Desi said she'd feel better if she looked like herself—or you know, if she looked like herself when she was in high school. Desi's obviously one of those creepy guys who never left his teen years and spends all his time reliving the glory days in his mind. He's also trying to convince her to forget Nick and just start all over—with him.
Now Amy knows she's made a mistake. She can't manipulate him. She can't control him. She can't get him to do what she wants. And now she's facing the consequences.