I think a legal separation would be a way for you to protect yourself, and considering the way the threatens, I think it may well be a good idea. I would also say that if there is a reconcilliation in the cards, a legal separation, in your case, is probably not going to be an impediment.
I would talk to a lawyer, and mention his threats (which I think he cannot follow through on, but the cost to prevent it may be high). Act from a position of knowledge.
