I would never become involved in any domestic dispute, regardless of the state, its a recipe for getting you in big trouble. As for what to do when someone is breaking in on you, I thought I was going to have to shoot an intruder this past week. I live in Texas and you have to know your state law. This guy came at 3:00 am, in the morning beating on my door. You can't shoot him for knocking in Texas. But if he is breaking the door in and he enters you can. I picked up my 45, made no sound. I turned the tv down and the guy knocked on another door, then he returned and started beating on mine again. I asked him what he wanted, never unlocked the door.
Right after he left, I called the police, and he was arrested in the next building. Turned out he was wanted for armed robbery, a number of assault and battery, plus sexual assault. The Chief of Police told me the guy was going to jail for a very long time and was a very bad guy. I think had I opened the door he might have grabbed for my gun.
I have a very secure door, but it could be kicked down. Now I am spending the money this month to put in video surveilance. He was unarmed, but whoever opened a door was most likely going to be robbed according to the police. The good news is the officer that made the arrest is moving into the complex near me.
But in some states, you have a duty to retreat, and may not be protected by a Castle Doctrine. I recommend you read over the deadly force statutes in your state and know exactly where you stand.