This technique I think over time will dissolve the split personality. Observe your thoughts, thought patterns, emotions, and actions. Observe. Don't Be that. Simply observe. It will bring you peace. The reason it keeps persisting is because you see yourself separate from this personality. When in actuality it is you. Same with internal dialogue or schizophrenia. It will all stop once you realize it is all you. Trust me. I know it might be hard to come to that realization. But when you do it will stop. I promise you. It might try to persist. Just remind yourself it is you. It will permanently go away over time. In my opinion.