Delusions are most often caused by schizophrenia. Paranoia, beliefs of being persecuted, making strange associations, a story out of a movie; we've got it all here. The whole point of psychotic symptoms is that you're not able to tell apart from reality from fiction, so saying that "you know it's not a delusion" has no weight. With relationship issues normal people are untrustworthy storytellers on good day because they present the events in a way that make them look like innocent victims of their partner or of circumstances. A schizophrenic storyteller? I don't buy it. I do buy that he's having a mental health relapse. It's funny how little the average person knows about disorders like schizophrenia.