How can I rid myself of masturbation and pornographic websites, and what should I do so that Allah does not expose me? Why was I exposed for what I did previously despite my repentance? And am I sincere in my repentance after I started smoking?

Sincere repentance from all sins, including smoking, is obligatory. This entails immediately ceasing the act, resolving never to return to it, and feeling remorse, while seeking Allah's help, associating with the righteous, and shunning the wicked. One must strive against their lower self, oppose whims, and be mindful of Allah's constant watchfulness, for Allah is aware of everything and is most deserving of awe. Listen frequently to beneficial audios and read useful books, and fill leisure time by memorizing the Qur'an and attending gatherings of remembrance. Let the motive for repentance be seeking Allah's pleasure, not fear of disgrace. Reflect on death and what comes after it, and on the horrors of the Day of Judgment. Know that deeds are recorded, and death comes suddenly, so beware lest your appointed time comes while you are persisting in what displeases Allah.