FWIW, self defense is typical a valid claim only when you are in direct and immediate danger, and that danger has to be death or grievous bodily harm. Danger or a potential harm at some nebulous time in the future--or danger at a period in the past--is not generally considered a valid reason for using lethal force. That's why women that murder their abusers often end up in prison; they typically kill their abuser when their abuser is asleep or otherwise incapacitated, rather than in the moment of being threatened or attacked. (Yes, I think that the law is wrong in that instance, given the dynamics of abusive relationships.)

Consult a lawyer for your state or province, because this shit varies from place to place.