I'm so sorry you're going through this.
I know you're grieving the loss of the guy you used to know, but at the moment, I think it would help you to keep a narrow focus on your immediate welfare and that of the kids. He needs to not be in that house if he's posing a threat to you and children. (You haven't mentioned violence but while he's that out-of-control he's not fit to parent.)
If he's refusing to leave voluntarily, it might be possible to get a court order to have him removed from the house temporarily--a family solicitor can arrange this for you, or child protective services. I'd recommend giving them a call to talk with someone about options.