you will have to face this obsessive person head on or run and hide. move, change all numbers, don't tell anyone, live a whole new life. or, go to the police and file a restraining order.
you might go to his family and suggest an intervention.
lastly, if this is not the first time this happened to you, what is it about you that is attracting this type of person to you? self-discovery and growth may be part of needed healing for you. best wishes.