displaying psycopathic behaviors doesnt make him psychopathic in and of themselves, atleast from a medical standpoint. granted if he displays a large number of them, then he possibly is...i was a medic not a shrink though, and mental disorders definately wasnt my specialty, do know a little bit though.
anyway, depending on what he did and how recently he got back, might just require time.
can u say what behaviors he's showing and what he did and how long he's been away from combat for?