You know, I usually don't even flinch at these "Sadistic love interest" stories...but I think this is the first time I'd ever thought to myself "So this is where we're really going with fiction, huh?"
It's like the bare bones of the archetype that has been oddly propped up into a story on NTR...-ish(?) material? At that point I don't think we're even in Sadistic Romance, we're just evil for the sake of it. And if Bro has been chasing and confessing for 11 years, we're beyond what could be considered NTR. Like at that point you're just exhibiting some creepy, stalker-ish behavior. Especially since she's actively talking about her boyfriends whenever you confess...for 11 years.
I think the idea is that she wants to manipulate him into having such an obsession with her that, if she were to date him, he'd obsess about nothing but her and have him all to herself... but dang is that the weirdest angle to take for that goal considering all the ways it could backfire. She MUST have been playing some 5-D chess all these years or something to keep this guy around.
Weird ride. Hope whoever this is for enjoys it, all I can say.