Anyway.. time will wash away everything ..
Basically usually those who rant and blast the most nasty stuff are the ones who will stay .. they will let it all out and just continue ..
It is those who don't seem to react and had nothing to say whom you worry about .. simply they will just fade and move on to something else ..
I think how much it affect a fan depends on the fandom of the fan ..
If the idol who have the scandal has become a representation of the fan .. it would be a very terrible thing for the fan ..
An example of the idols being the representation of a fan could be somewhat like .. the fan buy every single item of the idol, the fan meet her regularity for event to a point she remember the fan, the fan have her pic everywhere like on the wall at home, wallpaper of every device, everything the fan use are her goods .. from phone case, key chain, even stuff hanging or badges pin all over their bag, camp her social media everyday ..
Basically the idol revolve all around the fan life ..
And for these fans ..it will be a huge disappointment because they are on ready to include her boyfriend as part of their persona