A theory
This feels oddly personal. Neat group here.
I've always felt alone aside from occasional moments of companionship shared with friends or family. After digging around in my subconscious, I think two main "events" started me on the path. It is weirdly personal, so apologies if any of this becomes TMI.
The first event was my mother having a c-section. She was maybe 21 at the time, remained a virgin until her wedding day, envisioned a picturesque nuclear family as advertised on Leave It To Beaver. And her first baby was born weighing just shy of 13 lbs. Ow. The docs performed an emergency c-section (they tried to deliver normally to avoid giving "such a pretty little thing" a nasty scar) and left her with a large scar that ruined her self-image along with her hopes and dreams for the picturesque life. Her husband divorced her and her family blamed her for it. So, of course she was never able to accept me as her child. I was just the meatbag she was responsible for. I don't blame her for it, now that I understand the mechanics of how it happened. It makes me wonder, though, whether or not c-section babies might not have a predisposition for loner life styles.
The second event I think truly underscores the dilemma faced by single parents. I was about 4 and my mother returned home from work sick as a dog. It was probably a bad flu or something along those lines. Anyway, she didn't have a support network of any kind. So, she got sick and slept for 3 nights only rousing to use the bathroom. So, for 4 days and 3 nights I subsisted on saltines and water. I watched Looney Tunes. I waited in the living room wondering if or when my mother would die and relegated myself to keeping watch. Be damned if I can sleep at night 50 years later, still waiting and watching for the "bad thing" to happen.
Nearly dying another two times before I was 5 pretty much locked me in to an isolated mindset at an early age.
Thanks for reading.
The general question I would propose is this: does the loner life style occur "naturally" or is it a response to trauma? I doubt there's any single cause behind people becoming loners. It is curious though and I do wonder about the c-section thing.
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I don't know about the c-section theory, but your trauma definitely helped shape your personality and how you perceive the world around you.
Sometimes Loners welcome their solitude, while other Loners are forced by loss or isolation. It can be a blessing or a curse (depending on circumstances and predisposition).
Welcome to the Loners Group 
I choose to look at it as a blessing. Of course being an extrovert is also a blessing. It comes down to what you do with it, perhaps?
One more anecdote to round things out. Some 20 years ago my daughter and I were at a shelter in the wake of Hurricane Katrina. It was a surreal experience. A kind woman observed my daughter, age 5 at the time, quietly playing with a toy on her own away from the other kids and the woman said to me: "That child will never be lonely. She may be alone, but she's never going to be lonely." She wasn't wrong.
I think being a loner can be a good thing even in instances where trauma plays a precipitating role in one following a loner path.