“Are you threatening to leave me? Well then, let’s finish then.” Although it seems risky, it is the most dignified position you can show yourself..
Notice his next expression when he listens to you, whether it is surprised, defiant or fearful.
“If you’re going to threaten me every time we argue, then find someone who will put up with your threats, but I don’t have to do it or feel it.” These words will annihilate his toxic behavior and, if he really loves you, he will apologize and may choose to reflect..
Do not rule out the possibility that you can spend some time as a couple, which does not imply a breakup, but rather a valid phase of the same relationship.
Couples therapy is also another option that, although it is highly stigmatized, could be the most convenient way to end these types of threats and behaviors.