On the topic of the box-cutter thing. It was a very bad and stupid thing to do, but it's not that unrealistic if you keep in mind that the characters know each other better than the viewer knows the characters. I can see a very distressed kid doing something like that in real life, and their friend correctly believing they're not actually in danger. She wasn't coercing the other girl for sex, she was trying to do something extreme to get emotional closure.