Unfortunately he was raised in a cult and therefore if he tells his family about you they will go to the elders and he will be called to a Judicial hearing. At very best he will be told to give you up as a “worldly” girl and if he won’t he will be disfellowshipped and shunned by his family, his congregation his friends and everyone he has ever known. He will likely be thrown out of home, too. The chances are he will be immediately disfellowshipped if you have a physical relationship. They will view you as a tool of Satan.
your boyfriend is playing the long game and hoping to what we call “fade”. That is he hopes to become financially independent and slowly lessen his association with the religion. Given enough time he will move away and establish his own life and if he’s lucky they won’t go after him and he may, if he’s lucky, get to keep some semblance of a relationship with his immediate family at least.
He is in an impossible situation and I urge you to support him in this difficult journey if you truly care about his welfare.