It is not appropriate to diagnose someone, especially based on limited information. Diagnosing a mental health condition requires a thorough assessment conducted by a qualified mental health professional, such as a psychiatrist or clinical psychologist.
However, I can provide some general observations based on the information you've provided. The symptoms you've described, such as persistent paranoia, having two different personalities (which can be referred to as "split personality," though the correct term is Dissociative Identity Disorder), and talking to oneself, could potentially be associated with various mental health conditions. Paranoid schizophrenia and Dissociative Identity Disorder are two separate diagnoses, and each has specific criteria for diagnosis.
Paranoid schizophrenia is a subtype of schizophrenia characterized by delusions and hallucinations, primarily of a persecutory or grandiose nature, along with disorganized thinking and behavior. It is essential to note that the term "split personality" is not used in the medical field to describe Dissociative Identity Disorder, which involves the presence of two or more distinct personality states that control the individual's behavior.
It's crucial to encourage your friend Leo to seek help from a mental health professional if you are concerned about their well-being. They will be able to conduct a comprehensive assessment and provide an accurate diagnosis, if applicable, and suggest appropriate treatment options.
As a friend, you can offer support and encourage them to talk to someone who can help them understand their experiences and feelings better. Remember that mental health issues can be complex, and professional guidance is essential for proper evaluation and treatment.