I was thinking, what if "Chad's blackmail" is a still shot of the video mc took in the locker room (which would explain him jumping mc)and it says something like you tell sage or I will. But it was sage that did it trying to force him to tell her, but it backfired and chad decided to break up with her instead of telling her.
It seemed kinda strange she never showed the video to chad (mc even brought this up). Was it because he'd know where it came from? Or her trying to protect mc? Something else?