You cannot make the diagnosis of schizophrenia. There are many disease processes that cause these problems, including paranoia and "making up stories". One of the most common is Korsakof's syndrome, common in long-term alcoholics. They will have gaps in memory and "confabulate" stories, including meetings with another person that never took place and insults that were never made. I was involved with a Korsakov patient who complained to a physician how I was over his house and humiliated him and cursed him. The trouble was I was a thousand miles away on a vacation on the date in question. This incident was very real to him. Reasoning with these patients usually does not help. It is also common in Parkinson's (lewys body dementia). Often such patients cannot be convinced the ficticious events never took place. The big question is whether these halucinations are reversible. The answer is sometimes yes and sometimes no. In general the outlook is not good for these patients. They become more and more difficult to live with. Worse, the halucinations often cause them to go to the police with their paranoid delusions of non-existent encounters causing untold problems for a loved-one or co-worker. Certainly a good physical, including a neurological work-up, MRI and MRA are in order to rule out structural problems (such as a tumor or stroke).
I have a good friend ive recently been staying with until i get my new apartment and my aunt is schizophrenic. I know a lot about it and grew up around it everyday. I have Bipolar type 1 myself but schizophrenia is a whole other ball park and you will know if he has that problem. Its very very hard to have any kind of relationship with someone that has that problem. They will have periods of time when they are easy to get along with and they make sense but then long periods that are normally triggered or youll see it coming to where they dont even remember what they did. They go through psychosis and do very off the wall things that make no sense. My aunt comes up missing and ends up states away sleeping on the streets, fights with her loved ones but doesnt remember, accuses people of things they didnt do or say because people that have that disorder are paranoid and think they are being talked about, looked at, or people are plotting against them. At times if they get help when theyre doin well they will apologize but seems like they still dont usually remember they jus believe what you say. Other times they wont so to have a "normal stabel" relationship will be difficult but they can always be a part of your life. Hopefully if he gets help he will be on medication that works for him cuz thats a big thing and maybe everything will work out very well. Dont give up and encourage him to do what he needs to do so youns can be happy. If he ends up being bipolar then the chances will be better that things will work out. Bipolar is closely related to schizophrenia therefore bipolar patiants can go through psychosis as well.
How old is he? Generally the onset of schizophrenia takes place during the late teens to early 20's, and almost always by 30. I have a cousin who is schizophrenic and while she has episodes (when not on medication) she doesn't realize that she had hallucinations or was paranoid. Once she gets the help she needs, she realizes that things that she thought were happening really weren't. She's only had two really bad episodes, one just a couple months ago, but when she has them, she is overly paranoid. She is worried about her very loyal boyfriend cheating on her, people stealing her things, etc. She would go to random places and even filed police reports for the things she believed were being stolen. Both times she's been really bad, she has been especially religious as well.