†žBut of I turn him down who knows what he tells people“ - Like the truth. Damn jerk goes around telling people the truth!!! (Attention: Joke. The author of the comment didn’t intend to badmouth cheating stories, he just wanted to amuse the comment section community.)
"And then there's him", eh? Not exactly a great sign for her Kouhai, I suppose.
Also the title having 'Another Side' makes me think there's a prequel or 'other side of the story', as it were. Most likely from his POV, if that summary is anything to go by.
And yeah, turns out she was indeed being blackmailed by the other guy into sex and it's one of those where she just refuses to talk to her boyfriend about it.
If only she'd talk to him about it, I'm sure he'd be willing to do something to try and save her, but then again that's the sensible thing to do, and we wouldn't exactly have a release if things just got resolved quickly.
I honestly don't see this ending well. Poor guy will probably find out and be heartbroken, possibly leaving her, and in that sense she will lose one of the only people she seems to enjoy being around, which might push her further into just accepting being that other guy's sex friend?