Kimi to Scandal!

From Shoujo Manga Maniac:

Shiho is a big fan of Eiji, a very cool and charismatic singer. One day, he shows up at her door, with an announcement that he'll be living with them from now on... As her brother (Eiji, being the son of Shiho's father's girlfriend before his marriage)... Her dreams are rather shattered by the reality that Eiji really isn't as cool as he seems to be. When he has his glasses on, he's very huggy and cuddly and she doesn't like it at all. Eventually she starts to fall for this side as well, although it just kills his image.