SR-20 pilot reported a ground conflict while on approach due to another aircraft on the runway. Pilot executed an ATC-directed go around and returned to land.

Narrative

I was flying from ZZZ1 to ZZZ on an IFR flight plan. I was inbound on the RNAV XX in visual meteorological conditions (VMC) at this point and was cleared for landing. While on short final (within a mile or so of the threshold) a Diamond Star took the runway after being issued a Hold Short instruction from Tower. The Tower tried to raise the pilot but having no joy; issued me a go-around. I had previously completed my missed approach procedure briefing and the airplane was configured with the missed approach (MA) altitude bugged and repeating the mantra in my head of how to execute the missed even though I had no reason to believe I would have to do one based upon the visual meteorological conditions (VMC); I try to be consistent for safety reasons. I saw the Diamond Star pull onto the runway when the Tower told me to execute a go-around. At this point; I started my missed approach procedure of applying full power; simultaneously hitting my takeoff/go around (TOGA) button for flight director (FD) pitch visual clues; and began my climb on runway heading to 1400 feet while anticipating a turn direct ZZZ Vortac at 3000. ATC then asked if I wanted to execute the missed approach or go visual. Unfortunately; I chose visual which; in retrospect; was a mistake on my part. At this point I was in a nose up attitude and was not paying attention to the ground traffic as I *assumed* the Diamond Star had just blown his Hold Short instruction and it was a 'standard' runway incursion incident. My passenger was seated next to me and was leaning over the dash to see out over the cowling when she said 'He's rolling!'. I called Tower as they had not mentioned anything yet to confirm what my passenger was seeing. Tower confirmed and immediately approved a right cross-wind turn. I immediately executed while simultaneously registering my dissatisfaction with the Diamond to ATC. I then turned downwind but had not correctly monitored my reciprocal runway heading for right traffic and was extended out further from the pattern than I should have been. ATC gave me a heads-up and I told them I was not entirely familiar with the airspace; i.e. visual reference points and local customs. They were great and tucked me back in and the subsequent landing was uneventful. The ground controller suggested I call them to register a complaint. After shutting down; I spoke with the ground controller on the phone (who was actually the supervisor in the Tower that day) and he told me that in his 10 years at ZZZ1; this was by *far* the most dangerous pilot deviation he had seen.My Takeaways: What I think I did wrong: anticipating the unexpected and then not keeping to my plan in unfamiliar airspace. I learned to fly vast majority of my time at ZZZ2; which is just south of ZZZ3 Bravo [airspace]. Thus; I am very comfortable on the radios and in highly complex airspace. Prior to our trip; I studied the charts of the airspace in and around ZZZ and *thought* I was good with it. Whelp... that can go right out the window when the unexpected happens. In this case; my first error was accepting the visual in an unfamiliar area. What I should have done was execute the missed approach as that was what was in my mind and what I was preparing for. Deviating from that in a highly dynamic; high stress; unfamiliar environment is a recipe for mistakes as evidenced by my non-standard pattern. I will make sure to also brief a visual go-around in anticipation of similar; future events.Letting my emotions potentially cloud judgment. I'm not gonna lie; I was pissed off. I looked at the ADS-B data and it shows my altitude somewhere between 'surface/near surface' to 575 feet at the time I executed the go-around. Needless to say; that's concerning and I unfortunately let my reaction spill over to comms when I asked Tower 'Tell me you're taking a number on this guy?!' to which they answered in the affirmative. While I don't *think* my heightened emotional state translated into unsafeairmanship; as we all know; it is the *cumulative* effect of x-factors (here a Black Swan event of a guy taking off without a clearance at a busy controlled airfield; unfamiliarity with the airspace and heightened emotions) that is the problem. At a minimum; it was a net-neutral but also as likely a net-negative. One can't control how their mind and body instinctively reacts emotionally to a highly stressful situation; but one can control how they act once realizing the heightened emotional state they are in.I teach college and I constantly harp on my students that it is *never* a sign of weakness to admit when you don't know something or ask for help. Here; although uncomfortable to ask considering I had studied the space earlier; I told ATC I was unfamiliar with the airspace and; as expected; they were tremendously helpful. I did fully concentrate on flying the airplane first and foremost and never felt like I was not in control of the aircraft. My initial missed approach routine was spot on just as I've practiced a million times. Even after deviating by going visual and doing a wider-than-I-should pattern; I had a smooth remainder of the flight evidenced by my not-generally-thrilled-to-fly passenger saying that she was never nervous.