Move to Texas. It’s perfectly legal to carry a sword here. Doesn’t mean you won’t get some weird looks and questions, but you’re free to do it.
Depending on the state in which you live, your ex may have gotten away with keeping the gun because of you and other family members.
IIRC, brandishing a firearm is at least a misdemeanor in most state and brandishing as part of enforcing dominance in a domestic situation may be considered to constitute domestic violence. As such as conviction would have made your ex ineligible to own a firearm under ATF rules, which include a permanent bar on firearm ownership by a person convicted of even misdemeanor domestic violence, pursuant to the Lautenberg Amendment. You would have to check your state’s statutes but it’s not really a stretch in most places.