You almost have it, but you seem a little confused. I'm not the dev, so I can only explain what's been revealed so far. In other words, things could still change, but here's the rundown.
Lina was hurt by the main character in the past, and now she wants revenge. The exact details of how he hurt Lina have yet to be told. All of the women that the MC has had relations with are tied to Lina. With the exceptions of Mia and Chrissy, the women have been trying to manipulate him. The ASMR detail was a way for the author to tie Mia to The Studio (owned by Lina) without having her doing porn. I really don't think Lina cares about getting Mia into doing porn unless it might help her get back at the main character.
Fren isn't just an imaginary friend. He's another personality that the MC has (think Fight Club, if you've seen that). Mia talked about how the MC made up Fren to be the cool boyfriend for Mia that he thought she deserved.
As I mentioned in another message, how the Hell did the introvert MC that was pretty much a loner except for Mia found a way to hurt some rich woman he clearly didn't know before and that somehow his best friend never known about either? Its non-sense, also when I ask a question like this, its not meant to be a question to you, so much as an existential question, I don't question you, I question reality as stated in the narrative, I don't expect an answer I merely state confusion by venue of a question not meant to be realistically answered by anyone but the Dev but still stated more as a mark of exasperation.
Like I also mentioned in another message, basically its as if after Chapter 5 the Dev decided to create a completely new and different story, but chose to tack it onto his existing story no matter how much it doesn't make sense to be there to begin with, the MC is like 18 years old, fresh out of high school, before heading to college, how can some rich, adult, likely at least a decade older seemingly woman got hurt by the MC badly enough to arrange some nonsensical revenge plot over a nobody?
Its bullshit, no matter how the Dev stupidly swing it, did she somehow babysit him as a toddler and he peed on her and she swore eternal vengeance over that?! Neither him nor Mia recognize her, so for the MC to have hurt her it would have required it happening LONG ago, so he'd need to have been a lil kid at least, and if you as an adult swear eternal vengeance over something a lil kid did, you are too insane to be a functional human being.
It doesn't matter what sort of idiotic 'justification for being evil' the Dev try to pop up for her to keep her being somehow a LI, its stupid. If you don't question the fact this story has turned into utter non-sense in the last chapter you clearly lack some common sense yourself and are far too willing to let 'the Dev write the narrative they want' no matter how complete bullshit it is.
At some point their are to be limits and clearly at this point this story is visibly two separate stories melded together that don't make sense to be together, but the Dev didn't want to create new characters so he just tossed the new story where it clearly didn't work with the existing background and characterization.