Does the statement made by a person, "If I return a second time, then Satan is my god," constitute disbelief (kufr) when they subsequently resume the practice of masturbation, and what is the ruling on that?

A vow to abandon masturbation confirms the obligation to forsake it, and an expiation (kaffarah) becomes due upon returning to it. What this person said: "I am innocent of Islam" is a clear error and sin, based on the Prophet's (peace be upon him) saying: "Whoever swears, saying: 'I am innocent of Islam,' if he is lying, then he is as he said, and if he is truthful, he will not return to Islam safely." This statement does not lead one out of the fold of Islam unless the speaker intends disbelief. Scholars have differed regarding the necessity of expiation for this type of oath, and the more preponderant opinion is that it is not necessary. This person must make sincere repentance, frequently seek forgiveness, perform righteous deeds, and resolve not to return to what Allah has forbidden.