Hi, and welcome to our forums. From what you’ve described it sounds like a very typical paranoid type of schizophrenia - many of us have been there.
The important thing is to get him into treatment as quickly as possible. Like all major illnesses - the sooner it gets treated, the better. It will ideally include therapy and medications (generally as low a dose as possible - but you want to minimize risk of relapse, so its a balancing act).
Are you close to any of these early psychosis treatment centers - these are usually the best, and frequently free:
Let us know how it goes… you sound like you’ve learned a lot already - and are making the right steps to get him help.
I also recommend you read this “first aid for psychosis” page on our site - so you understand how best to deal with your fiance when he’s psychotic: