Is there any way to complete Cassie's arc without doing all of the torture stuff with Fawn, because I really want to help Cassie but I equally want to avoid everything with Fawn.
'Torture' is a harsh word, it is a Play, BDSM is not Sadism, Fawn only satisfies urges after 'Toying' with you.
And No I dont think you can.
If you can't handle Masochism you might want to save the Future or Arlene, for last.
You only need to know that she works at the club to be able to complete Cassie's route. You don't need to become her subbe