Summary Scarlet from Kainu Manga
Scarlet summary: From Blissful Sin: College student Akio is dating his beautiful classmate, Ryou. Unable to stand the slightest loneliness, Ryou accepts any girl who approaches him. One day, Ryou introduces Akio to a girl he is thinking of marrying which makes Akio decide to completely break it off with Ryou. Instead, a heart wrenching love story takes stage!