Koisuru Hotaru to Kurashiteru

The high school girl Suzu Mayama was forced to stay with a friend of her mother's while her rooming house was being renovated. However, her friends mother has son, who turned out to be her classmate Hotaru Saeki, a downer type of boy. Suddenly living together, they didn't want to tell anyone at school. He's hard to get to know, but under the same roof is the perfect distance for love... (Source: Comic Pool, translated)