Ok I just see a lot of fanart of AraSol shipping where Sollux is all upset and holding her dead body after killing her. But reading a later pesterlog (Sollux: Deal with apocalypseArisen) Sollux doesn't seem to know that she is dead at all. I'm not sure though....?

Sollux might not have known.

But you have to remember that Sollux could hear the voices of the dead so even if he knew nothing would seem strange when he could still talk to her.

Or he just knew that she was a ghost.  I dunno.  Feel free to correct me if I’m wrong.

~Mod T

EDIT: Excuse me, Aradia heard to voices of the dead, Sollux heard the voices of the imminently deceased. Thank you tumblr user glaceonprism.