For your own safety and protection, could you have a friend or someone come over the house to be with you when he is given the letter or when he is told to leave the house? This may calm your fears of it escalating to needing the police. I understand explosiveness, and it is scary to deal with. Fear should not stop you from kicking him out though. IF he does explode, just quickly leave the room, leave the apartment, and call the police immediately. You will be safer that way, if you leave the situation and let the police handle it. But I think having a friend or someone to be there with you should also help calm your fears.