
Quoting
Mr. Knowitall
You were in a federal courthouse, and therefore there were federal law enforcement officers and court officers providing security at various locations in the building. It would have taken you all of fifteen seconds to find one. You appear to be confirming that you did not take the threat seriously, did not report it to anybody, and aren't going to share the back story... so there's not much we can say.
If you're terrified of the person you live with, move out, seek a personal protection order, etc.