Is sexual deviation a sin or a psychological illness, and is it possible to completely rid oneself of major sins through sincere repentance and religious commitment?

It is obligatory to guard one's chastity except with one's wife or what one's right hand possesses. Transgressing beyond that is forbidden, and whoever does so is sinful and an aggressor, as Allah Almighty says: "And those who guard their private parts Except from their wives or those their right hands possess, for indeed, they are not to be blamed But whoever seeks beyond that, then those are the transgressors." To avoid major sins, one should distance oneself from whatever incites the soul towards them by diverting one's thoughts from them, avoiding the company of those who commit them or going to places where they occur, and occupying oneself with beneficial knowledge, work, or sports, and associating with righteous people.