Firstly: this boy is just really edgy, he doesn't know how it feels to actually wanting to kill someone, you learn about human muscles, human anatomy, and if you're finished you create the most painful slaughtering method (psychological pain included).
Plus he's a simp if a girl took my knife e I would have forced her to give it back to me, because my knife is part of my stuff, and you don't wanna know what happens to people that take my stuff.
and also why did he take HER trash to the trashcan, if you don't like her show her that you don't like her, that was everything, i still think this story can get better so imma keep reading and if it doesn't get better, I'll stop reading.