Bump here too.
In my DUrge playthrough, my character decidedly chose to keep his urges secret. I never picked any conversational options to talk about the urges. Never ever! Also, I left everyone behind when I actively went to kill Isobel after creepy dude told me to. And I made it a point to NOT use Slayer form in front of any companion.
Queue my surprise when Astarion out of the blue just went: "So, you are the Slayer now." Or something along those lines. I mean, TF?
Same after the Isobel kill. Suddenly all companions just gave me flag for killing her. Again, nobody was in that room besides Isobel and I! No witnesses! And I most definitely didn't tell anyone!
Yet, somehow magically they all just knew right away? They knew I killed Isobel, they knew about Slayer-form, knew about the urges...
That was VERY immersion-breaking and disappointing. I think, no companion should know about my dark sh*t unless I CHOSE to tell/show them.