Is a person possessed by a jinn lover, who practices masturbation and is addicted to pornography, considered a disbeliever (kafir) as in His saying, the Almighty: "Our Lord, some of us benefited from others, and we have reached our term which You appointed for us. He will say, 'The Fire is your residence, wherein you will abide eternally'"?

Jinn possession of humans is a reality. There is no sin upon the one who is possessed by a jinn for harm, but he is sinful for the acts of disobedience he commits by his own choice. This is not considered disbelief. It should be noted that much of what is thought to be possession is not so, for people often follow their desires and whims. As for the noble verse, "Our Lord, some of us enjoyed one another," it is not from this category. Rather, it speaks of humans using jinn and offering sacrifices to them, or of some of them obeying others. The stratagem of Satan is weak, so whoever sincerely seeks Allah's help will be freed from what afflicts him from Satan's stratagem and touch.