How do you tactfully break up with someone who just doesn't seem to "get it"?

If your boyfriend lived with you, then he owed you part of the bills for his own upkeep. You do not owe him anything. Do not let him laugh you off. Turn off the TV, eliminate all distractions, sit down with him and tell him that you no longer want to be involved with him, your relationship is over, and he must leave your home within 30 days (only because the law requires you to give a tenant this much notice). I know you don't want to get the police involved, but you may have to, depending on how serious this guy is about staying or hurting your crush. If he does not leave, file eviction papers against him. Then regardless of anything else, get a restraining order against him just in case he shows up again. Talk about how he refused to leave and said he wanted to kill your friend and his parents, and felt homicidal at the sight of the actor, to show that he is unstable and potentially dangerous, and you should be able to get it.