So what actually happened at the end of Volume 8? Who won? Kirino or Ruri? Unfortunately, there are differing accounts of what happend all throughout the Internet. Rumors of Ruri moving (but then coming back) and torn up light novels by certain Ruri supporters. Combining all the conflicting reports led me to this unofficial summary of what actually happened between the three.
"Kuroneko dumped Kyousuke after he did/said something involving his sister (nothing sexual) and it made her realize he won't ever love her the way he loved Kirino.
Which then became public knowledge on campus (Kuroneko did rat out Kyousuke's relationship with Ayase to Kirino during the Oreimo PSP's Ayase route, so this is no surprise) everyone gave him the cold shoulder.
Out of nowhere, Kirino comforts a depressed Kyousuke over his break-up. To the point of him saying "Damn! If she wasn't my sister, I would've fallen for her!". While Ruri dumped him because she thought he loved Kirino more, what she did indirectly set off a now much more complicated relationship between the three.
End Volume 8"
As for the rumor Ruri of moving a way, certain Ruri fans claim it was only temporary and she actually ended up moving closer to Kyousuke.
No girl "won" in the end of Volume 8. But Ruri's abandonment of Kyousuke because she thought he had stronger feelings for his sister...indirectly resulted in him beginning to see Kirino as more than just his imouto.
This is very important since while we have always known that Kyousuke truly loved his sister, this is the first time that he himself actually started considering looking at Kirino as more than just a sister. We know that as the series progressed that Kirino herself started developing strong feelings for Kyousuke, even to the point of forcing him to go on an actual date with her in Volume 6. But while Kyousuke's relationship with her improved, it only showed that he truly loved her...as a sister. He may have had other feelings for Kirino, but it is at best subconsciously. It is only at the end of Volume 8 that is beginning to consciously realize his feelings for Kirino.