Our heroine's name is Kareigawa Shiori. If you take part of her family name (kare) and given name (shi) you get her nickname (kareshi, or boyfriend).
I know this is going to get removed soon, but while it's here, is the tagging accurate? Who's being stolen? The brother, or the friend? If his sister is a brocon, then yeah, male:netorare makes sense, but without added context to those final panels the gist I got was that she was lamenting Shiori picking her brother over her. Is there a sequel (or even a prequel) that adds context?