I've literally haven't discovered Ste yet do I need to befriend the lady underground or something
After you freed Korg, after a while you can free Ste but this time you need to fight and win against the succubus.
I let Korg go
There's no need to fight her if you can bring somebody who can satisfy her
That is also an option. I did not choose to bring her Arion (also bc I did not know is possible)