You can think you can handle something or that something is a good idea at one point, and change your mind later. The first one was a gangbang. ALL the other ones after she didn't want to do it anymore (because she didn't really care about him anymore) and they threatened to (or actually did) release photos or videos of her, were gangrape.
Being susceptible enough to agree to a sex act you don't want to do so that someone will like you more is such a common experience for plenty of young (or old, sometimes) people. I think the story is saying that she had 2 goals: get out of sex slavery first and get close to Yuuma second. And to be fair, we've been getting subtle hints that she wants to get close to Yuuma all this time. That said, I also hate this plot twist. I think it's unnecessary melodrama and doesn't really change the fact the dude is a gang rapist.
true. it feels like the author is trying to posit yuuma between her and ameri by making her out to be as bad as ameri when that's really not the case given the information and why it feels so off; i think it's a fun concept to have yuuma between two evils but she's really not evil...
as you said too, the "twist" here doesn't change the fact that guy is a rapist and wanted to see how far he could push her and for how long, and continued to do it when she did finally get the courage to run. he took advantage of her personality to do what he wanted to be with him.
that being said, i think the t/n constantly calling her a bitch is a bit much, when ameri is doing just as manipulative shit to yuuma.
ameri is my favorite to be clear, it's horror fiction and i'm mostly here for the BL aspect lol, but it feels like real world misogyny has leaked into this arc even with a good faith reading of it.