Just a few considerations about the 'blackmailing' thing. Yeah, there's no ground for any legal action against the MC. And yeah, it doesn't really matter.
Tybalt is not threatening with a lawsuit, he's just telling Jill someone else is willing to do so and he's going to stop that person. For that lie to work, he only needs Jill to trust him enough to take his word for an undisputed truth and not consider taking matters into her own hands and talk directly to that person. He also embellished MC's acts (he keeps talking about a fire that never happened, and if MC had punched him he omits his own slap) to show her MC is not a person suitable for someone like Jill (which she obviouly believes if MC told her after their first date that he's not good for her, cause then Jill never calls the MC when practicing for her concert and never goes on a second date with him). That 'mild threat' is just a way to convince Jill to not hang out with the MC because he's trouble (which, honestly, so far he is). He just says, "look, this guy did all of this, and a certain someone wants to sue him. I'll convince him not to do so, but you should start to take care of yourself and stop seeing a troublemaker like the MC". And, honestly, I can see why this could work even if the lawsuit thing is just a bluff.
So the whole point is not if there's a base for a legal case, because it will never be a legal case. The point is why an in-love Jill can believe Tybalt to that extent when he tells her there's another prep willing to sue MC. It's not a plot issue but a Jill's characterization issue: how can a girl like her believe a guy like Tybalt when she feels something for the MC? Why she believes Tybalt is going to convince that other guy and lets him do so, instead of taking matters into her own hands and clear things out with the MC and that other guy first, to know what exactly happened and what are the future consequences of it? Because she just accepts Tybalt's word on it and even when she 'rebels' against his advice and invites MC to the birthday date she's apparently decided to end things with him before knowing MC's version of the story. She was always presented as a nice, caring and inteligent girl, and now she seems to be not just naive, but socially dumb and unaware of the whole world of possibilities her surname opens to her. Which is not to be expected from someone with her background.
Because, as in Maya's case, why nobody ever consider asking for profesional help/advice when facing a legal/financial problem that goes beyond their comprehension? That's something I could believe from someone like Maya, or even the MC, but it's harder to believe from a rich girl who should be used to be around lawyers all her life.