Jack or Alex

Schizophrenia could be the case? Perhaps Nigel noted Alex' schizophrenic behaviour and hence called his obsessive side Jack, whom Nigel knew was willing to do things with him...
Why would we see Alex tell Nigel to get out of his room, but later on agree to follow him to his house.. Quietly and obediently!
Nigel knew jack as he knew Alex and so told his parents of his 'better friend' Jack rather than Alex....
Open to counterarguments!