I have installed decorative stone in some of my walls, I really like how the look like, though the pictures don't make justice, but I'm not really happy with the edges since I don't have a wall that covers the sides. The sides look like the stones have just been cut or put in there like a 3D wallpaper.
One of the walls, the most noticeable that is on the entrance of the condo has just a closet on the side, picture attached for more context.
Best Answer
I'd install some wooden trim / decorative moulding and paint it to match nearby woodwork.
Make the left vertical edge of the decorative-stone even by cutting where needed (e.g. middle row of upper photo).
tack/glue appropriate sized stripwood behind front edge of moulding as shim.
Attach the shimmed moulding using adhesive (as presumably used for the decorative-stone)
Paint
(I'd also grout all those stepped joints)
Another option is to continue the decorative-stone a short way around the corner - some manufacturers of these types of panels allow for this. (random example)