Oboreru Vanilla

Nanao has always kept her feelings for her sister's boyfriend a secret, but one night, he drunkenly spends the night with her?! Two years later, still haunted by regret and unable to move on, Nanao drowns herself in a superficial relationship with the mysterious and handsome Haruto. Just as she tries to forget the past, it comes back to haunt her when a man she never wanted to see again reappears... (Source: MangaPlaza)