Yes, Sorin is completely insane and the longer he goes on killing freely without help he will just dive deeper into insanity, I suggest talking to him and asking him stuff.

[quote=@OfficerHeadbutt]
Atlas has a flare for the dramatic and an evil happiness to him. 
Sorin should be more dark and brooding.
[/quote]

Sorin is a very calm and blunt person other than his laugh or when he is pissed off if that's what you mean.