I really hate it when some third wheel shows up just as we're about to get a nice conclusion. Especially when its the last chapter.
You might be confused there, the last character introduced is not trying to cut into any romantic relation (the sisters (not rly sister) only have a one-sided-overly-attatched relationship, as a result of trauma). Unless third wheel just means another character is tagging along the group, which would make it a fourth wheel?