Oh, I wouldn't worry so much about that. Knowing her personality and her obsession with him, she'll likely to go all 'Happy Sugar Life' on her idol friend if that ever happens. Well, I guess that would be one way to solve it...
Didn't see that one coming, but I think this is character progression...?
The first step to recovery is admitting you have a problem, and she did kinda jump the gun in assuming he was the one stalking her. I hope she gets proper help to channel her emotions healthy and get a group of people who will support her in doing so.
Please no. I hate the yandere psycho lesbian arcs in manga, and this series has enough unlikable characters as it is @Hollow7F
If she did call the police, and check the tenant records, they would see he has lived there longer than her.
Also, just because he wears a disguise at the concert, he is automatically a stalker? Maybe he is embarrassed or something you stuck up bitch.