I am looking for a name of a manga that i read once. The story is about two lovers who have been together for a few years. One is still living with atleast his sister. One day the lovers have a small spat over not being able be together cause their relationship is a secret. The sister leaves to her fiance house for the night and the lovers get together. Sister comes back early and finds her brother with his lover. The story continues from there......

Thank you for any help in advance......