I confronted a burglar who was outside my house, in the process of jimmying one of my back windows with a big flat-blade screwdriver. I saw what he was doing (the lights were off in that room*), flipped on the light, aimed my 1911 at him through the window, and yelled at him to get lost. He barely even hesitated before spinning around and bolting. I'm about the same size you are, but I wonder if he even really noticed anything but the pistol.
I too would be horrified to kill another human being. I would shoot to defend myself, but if the person died, it would still be an incredibly traumatic experience, regardless of how justified my actions were. I don't think any sane person really feels differently, for all that some may bluster about "the scumbag deserving it."
I think it's important to note, however, that what happened in my case was very much a legitimate "defensive gun usage." The guy may have skedaddled just as fast if I'd been unarmed (like yours did), but that's not a given. Some pretty good research indicates that the majority of defensive gun usages end like that: crime prevented but no shots fired. The assailant backs off in the face of potential deadly force being used against them.
*In fact, most of the lights were off, as I was relaxing in my basement reading nook. I am certain he thought there was no one home. That incident prompted me to leave a visible light on upstairs when I used that room. I'd never considered that before.