Is the practice of masturbation and watching pornography, while adhering to acts of worship and remembrance of God, considered a sign of mental illness or a split personality? And what is the way to overcome this desire?

This vacillation is not a psychological illness; rather, it is a struggle between piety and depravity within the human self. The cure lies in increasing acts of obedience, distancing oneself from sins, striving against the self, and enduring with patience. This necessitates applying the Prophet's (peace be upon him) advice to Mu'adh (may Allah be pleased with him): "Fear Allah wherever you are, and follow up a bad deed with a good one, it will wipe it out, and behave with good character towards people." This advice is comprehensive, encompassing the rights of Allah and the rights of people, and guiding towards the erasure of sins through good deeds.