How can one overcome the addiction to watching pornography, masturbating, and thinking about sex, knowing that I am a committed young man who observes prayers, recites the Quran, and performs adhkar, and yet I suffer from constant sexual fantasies and difficulty getting married at present?

Do not despair of repentance, no matter how often the sin is repeated, for Allah accepts the repentance of whoever repents. Make your resolve to repent stronger than Satan's insistence on dragging you back to sin. This situation is considered an addiction, requiring psychological and spiritual treatment through supplication, morning and evening remembrances, and establishing prayer. There is no harm in visiting a psychiatrist. Among the aids to quitting are: avoiding solitude, lowering the gaze, seeking righteous company, and seeking refuge in Allah from Satan when temptation arises. Hasten to marry if possible, otherwise, you must fast.