What is the way to get rid of the addiction to masturbation and pornography, and to sincerely repent from zina (fornication/adultery) which Allah forbids me from, especially with the belief that watching pornography leads to doctrinal deviation and atheism, and with the fear that repentance may not be accepted due to illness and a weakened ability to commit sin? And does persistence in masturbation make it a major sin necessitating eternal hellfire and nullifying good deeds? And is it permissible to use social media sites that may lead to forbidden relationships?

The imperative is sincere repentance from all sins. Repentance is sound and accepted if it fulfills its conditions: abandoning the sin, resolving never to return to it, and regretting having committed it, even if it was due to inability or illness. Every time you sin, repent, and do not despair. Persisting in minor sins, such as masturbation and watching forbidden things, turns them into major sins. You must avoid looking at forbidden things because it can lead to Shirk. It is not permissible to use social media to establish relationships with women. You must be wary of adultery and flee from it. Accompany the righteous, adhere to remembrance [of Allah] and supplication, and avoid what incites lust.