What you did wrong was choosing the option "It's more important to stay," you HAVE to, and I mean HAVE to, leave to put up posters for your brother, even if this results in your love interest getting upset with you, this is part of the story that is non-negotiable. This is a MUST. Lol, try it again choosing this option, and if it's still wrong, then scroll through the comments, there are some walkthrough's that me and other people have put in the comment section.