be as nice as possible, but your happiness is your first priority. if he is an adult, it is his life, there are other fish in the sea, as they say. if you think he is really serious, and not just trying a tactic to keep you around, contact the authorities after you break up. especially if he continues in that direction. if he threatens you, definitley go to the police. there is no way to soften the blow. i really believe this is probrably just talk on his part. if you do break up with him, make it a clean break, no contact afterwards, and move on with your life.