"Slut Holly" is a result of Ivy taking control of Holly's life and convincing her to have casual hookups and other ways to entertain herself without commitment. Holly who is in a dedicated relationship (be it with Ian or Lena) doesn't fall under this influence so her personality shapes differently.
Well, Holly can go to dancing classes, sees Lena as an inspiration and to a certain extend Ivy. If the Ian we play is interested in experimenting (many lust options and/or threesome with Alison), wild Holly and this type of Ian might be a perfect fit.
Well compared to Cindy Alisson is safe if you choose her she wont cheat on you
One slip from Ian and she became a cum dump of Jeremy then gets double dicked by sleazy producer guy. Do you have any proof of Cindy's doing? Because you get proof of Allison's.
That very much depends onhow you play this story arc. It becomes quite clear during it that Alison goes for Jeremy and the others only if Ian does not see her swung sign "I want to wanna be with you". If you and Alison couple up, from then on she is very loyal and only "does" Jeremy if the player wants her to (wild Alison girlfriend route).
To get the wilder Alison but in a relationship with Ian (even then she is loyal after you two couple up during the weekend holiday), you have to let Alison get together with Jeremy one or two times and then fly in and go after Alison hard. Once the two are a couple Alison is, as said before, very loyal and only does other guys if the player really wants this (e.g. the future second threesome).
Cindy on the other hand seems to not even know how to spell loyal.
