>>2505808They didn't break up, it actually ended with Kyousuke finally managing to get Kirino to accept her feelings for him. The ending had to have some ambiguity because of the retarded censorship laws and the publisher's editorial policies.
Fushimi gave Kirino and Kyousuke the best ending he could get away with and dropped hints all over the place that they will stay together. Of course that's far more obvious in the novels and the anime did fuck that up a bit by changing the kiss,
which was supposed to be on the lips, and many subs screwing up an extremely important line (the renewal of the life counseling). To make it 150% clear the siblings are still together in the After Story that takes place 6 months after the epilogue.
Spoonfeeding pastebin, just skipp to the spoiler section:
http://pastebin.com/g1awYmW4 
