Schizophrenia or Paraphrenia

I want my main character, Brandon, to have a mental disorder. Schizophrenia is a serious mental disorder, people with this condition tend to have a different perception of reality combination of hallucinations, delusions, and extremely disordered thinking and behavior that impairs daily functioning. Paraphrenia is a mental disorder characterized by an organized system of paranoid delusions with or without hallucinations. 
The difference comes to the age range which affects. Paraphrenia affects elderly people and schizophrenia can affect people from their early adulthood. 
Since Brandon is imagining his friend all his life, for him to show symptoms of schizophrenia he would have to show changes in his mood, hallucinations (of his best friend), and sudden changes of behavior. 
People with schizophrenia often have speech symptoms like incoherent speech, rapid and frenzied speaking. Also a lack of emotional response and fatigue are often seen. 

Delusions and Hallucinations 

Delusions and hallucinations aver very common in schizophrenia. Most of the time, people with this mental disorder will experience auditory hallucinations, like hearing a voice or many voices. This a combination of positive and negative symptoms for schizophrenia. 
In this case, Brandon would have a combination of all, auditory, visual, olfactory, and tactile hallucinations.