Lots of hugs and kisses from everyone PinkFizz and the answers are all the same, call the police and tell them what's happened, you and your child are what's most important and I am sure your bf will see it that way and obvioulsy doesn't care about his job as he's told you to contact the police as well.
Your ex sounds very irrational and as much as I am not trying to trivialise what he is saying, people who say what they are going to do to you etc etc normally don't otherwise they would just go out and doing without any warning. He's obviously trying to intimidate and frighten you and your bf and it's understandably working. Despite this I would still speak to the police, that way you will feel safer.
Try and get someone to come round or get yourself out and about to help keep your mind off it.
Hope it all works out and your take everyone's advice, after all, it's not safe for your son or bf either so act on it straight away.
Take care pumpkin x