Okay... The guy is an asshole, sure.
But frankly I can't even get angry when Banri was such a dumb idiot here.
You are telling me she let herself be pushed around, treated badly, and possibly molested/raped because that dude knew they weren't blood related siblings?
...so what?
Why the fuck does that even matters? Is not as if they being all adopted is something that scandalous.
Sure some other kids would be assholes about it. But the whole "haha your real parents abandoned you/are dead" stops being a good bullying line when the orphan gets adopted by a rich family.
Damn, glasses dude could even get sued along the magazine if they published an story about it.
So she only fucked her own life just because.
Even worse, Arata asks if they were really dating and she doesn't answer but says the dude entered her phone, referring that he possibly read some messages and that's how he learned about the whole adopted siblings thing. And she says that she thought they would face the situation positively as lovers.
So apparently is not that he extorted her into dating, but that they were dating already.
Because the alternative is that the guy -a friend or acquaitance at the time- spied on her phone and randomly extorted her into dating... So what she expected? She really thought he would be a good guy despite that?
Ir doesn't make sense, Banri is stupid and deserves every bad thing that happened to her.