OK, I was wondering if there were any good series with a certain relationship dynamic similar to Kyousuke's and Kirino's from Ore no Imouto ga Konna ni Kawaii Wake ga Nai (Novel). Specifically, a girl used to be very sweet and close to the hero, maybe even clingy and doting, but for some reason now she treats him like dirt, and either no reason is given or the reasons are superficial. Doesn't have to be a romantic relationship, a guy regaining some of the purely familial love of his sister is great on its own without that sister wanting to break taboos, and it's also sweet to see a guy just go back to being friends with a girl without making her his girlfriend. Doesn't matter whether the two have stayed in touch all this time or not; there's a bit more impact anyway for a guy's last memory of a girl being that sweet and caring young girl and then suddenly he's faced with an absolute jerk who hates his guts.

The only thing I can think of besides OreImo that fits this Kimi wa Midara na Boku no Joou, but that one was discontinued, not to mention that it's incredibly close to the 18+ line and its revelation is almost immediate.[spoiler]The hero was separated from his childhood crush because as the daughter of a rich family she was to go to a high-class private school. Not wanting to lose her, the guy spent years studying his butt off to get in on scholarship by high school, but when he did not only was she completely different, she treated him with absolute contempt. However, like I said the reason and resolution was almost immediate, as both wished to become closer and wished for their rooms to be joined, and a "god" granted the wish in exchange for the girl losing all self control for one hour each day. The first thing she does after losing it is to express how much she's always loved him, how she tried to become ladylike to impress him, and how she's too embarrassed to be open with him outside resulting in her contemptuous appearance. Then things break down as she starts to reveal other aspects of her desire for him and how little control she has over it. Like I said, it's incredible how close they're able to come to that 18+ line without crossing it.[/m]

Pride Complex fits. Though the two remember that they hated each other as children before remembering that they were actually friends.

To a lesser extent, Masamune-kun no Revenge, though the girl doesn't realize the guy is her childhood friend.