I understand your gripe with the choices, but the Prologue and Chapter One follow a linear story in a sense, but the choices will affect the endings.
More choices will be included in Chapter Two which will affect the way scenes play out to give them different variants.
As for an English native speaker, I'm embarrassed to say I am one... My writing isn't the best though. I sucked at English GCSE haha.
I'm really torn with this title. There are a lot of aspects I really like. It appears you intend this to be a fairly sophisticated corruption story. I don't know where the therapist sessions are going, but it would be really refreshing if not all the men are ethically challenged, assholes violating their Hippocratic oaths. Yes, I know these are corruption stories, it just gets draining that so often the "alpha" men aren't really alphas they're just creepy assholes raping and sexually assaulting women.
Anyway, I have two difficulties with the narrative choices you've made.
1) As some have already mentioned, the story ends up being very linear with very little real choice. You're forced into a circumstance regardless of your choice. That's not very satisfying from a gameplay standpoint. You say above that it will have an outcome on the ending, but that's a long time to wait for resolution. Unfortunately, that also means that the only endings possible are driven by Isabelle's resistance/voluntary choices early on. Many people that go down a dark corrupted path may still decide to change even if they voluntarily chose that path early on. So, making a reform ending based on earlier choices to resist precludes the possibility of Isabella WANTING to change, even if she voluntarily chose to do those things early on.
2) There are many paths to corruption and even mild voluntary corruption may cause nightmares. What I mean is that even if the person only becomes half corrupted, Isabella could have different tolerances depending on how the gamer wants to play it. They don't have to see all of the corruption to end up with night terrors. Night terrors can come from failed or successful efforts at rape and coercion. The changes in what you do merely affect the therapist's advice.
Even an unsuccessful rape can traumatize someone and cause them to act out as they question why that person tried to rape them. Is there something wrong with me? Am I really a slut? I resisted and they don't love me, do I need to become more compliant and slutty to make them love me? This happens to people with poor self-esteem all the time. Choosing not to do the dating side job doesn't have to be coerced right away. Olivia can say "Whatever! Do what you want to do, just ask me later if you change your mind" and then she can either start acting a little more cooly toward her, or there may be financial reasons later that causes her to ask about the job. Maybe her parents have financial difficulty or Mason causes her financial problems. There are lots of paths to her doing the job.
It feels like you didn't consider the possibility that they may voluntarily choose a path in its entirety, regret it and then choose to change and become less corrupt or to entirely resist the path, be traumatized, but then choose to embrace the corruption anyway.
Early choices don't have to dictate the ending. Any of these paths can cause the person to either choose to accept the path they have chosen or change and go a new direction. A lot of it may depend on how you decide to play the therapist. The therapist can point out how those voluntary choices or resistances may be affecting her psyche, her relationships with other people, the problems it may cause down the road and how it will inevitably affect family, and then tell them that the path they choose will ultimately be their own. (getting into a polyamorous relationship will close off relationship possibilities with some, but open them to others--it depends on who they want to be, just as being gay will do the same.).
Think about it, because you don't have to force gamers to do X, Y, and Z to have a story and your story is good. The prologue with her expressing her desire to become more open was excellently done. But in the end, you could have Isabella just do X and Y or just X and she could still be driven to a therapist to deal with night terrors that arose from doing X, X and Y, or all 3. Many players will choose all 3 just to see all the corruption and sex scenes, but others will want to explore multiple paths to see different outcomes. It increases replayability.