First, Ayase plan since the beginning was to marry Kyousuke so she can finally become Kirino sister, stupid dream but it's a 14 years old girl dream. Thanks to the whole issue with Ayase discovering Kirino hobby the whole image of Kyousuke got broken, yet he proved without a doubt how much he cared for Kirino. After this Ayase and Kyousuke becomes the best "pals" since Kyousuke didn't give a fuck anymore about appearances, they become more and more closer throughout the series with Ayase still holding onto that dream despite everything, during this time(almost two years) Ayase feelings start to change, she fully trust Kyousuke and her plans start changing, its not anymore about Kirino anymore but about this reliable senpai in front of her. Still unsure about this feelings she just spend more time with Kyousuke as a "friend", this go on till the whole stalker issue happens, and in which Kyousuke saves Ayase finally making her fall for him, the rest is story, after all, the dream never stopped being a dream.
And this is a very bad summary of all that happened, I mean, do people just pretend to be stupid or they actually can't keep focused in a simple story? Also, this thread sucks.