Dave876
Although the laws differ from jurisdiction to jurisdiction, most say that there has to be a percieved imminent threat of bodily harm to use deadly force, i.e. fear for your life. If you do buy a firearm, make sure that you both learn to use it and become proficient with it. How you TRAIN is how you will REACT, should something (God Forbid)happen to either of you.
If a firearm is not the answer for you, mace, folding , martial arts might be an option. Hope this helps.