Shinonome Yuuko wa Tanpen Shousetsu o Aishite Iru

From MangaHelpers:
Minami Eita lives with his older, book-loving brother, whose long-time girlfriend Arumi is often around the house. Minami tries to get along with Arumi, but the truth is that he likes her much more than is appropriate. Even though Minami doesn't read much, he helps in the library with his bookworm classmate Shinonome Yuuko, who loves short stories. She thinks that while most people want to think of themselves as the hero of an epic saga, short stories are much more like their actual lives. Minami's ordinary life becomes more confusing when he begins to suspect that he has feelings for Yuuko. One day, he finds out her secret--she is actually a published author of short stories! Her publisher wants her to write a novel, and she has enlisted Minami's help in an unexpected way. Minami's teenage life is not going to get simpler anytime soon.