Small guess: you never pick up the phone on first time unless you've been expecting a call or think it might be extremely important? Then you always ring the person back at your own leasure?
Actually, that might not be the case for you (although it's very likely...) but congratulations, you are introverted!
Which is really not the same as anti-social, believe me. I recognise everything you write about. Down to finding quiet spots during parties, preferring alone time and the 'struggle' to fit in. The good thing: it's not some social defect. Introversion/extraversion is just a black/white term for something (far) more complex, but essentially we introverts (a whole bunch of people, most of whom spend a long time fighting their nature) charge our batteries in different ways. I know people who go to parties to talk, dance (*shudder*) and 'have a good time' and their idea of this 'good time' is my own personal 7th layer of hell. It's absolutely exhausting for me to be around a lot of people; talking about nothing; pretending to have a good time. My battery gets charged being alone, talking to a single person in a quiet environment, or just plain ol' spacing out and looking at the clouds.
At the same time I have a great career, a ton of ambition, a nice girlfriend and I'm seen as a social enough person by my colleagues. There was, however, an entire spell during my early twenties where I completely shut myself off from my surroundings. I just could not be bothered to play the 'social game'. The trick is to find a nice balance; to know what you can, and can't do (socially) without getting bored or uncomfortable enough to become unhappy. An example: at some point I started telling friends that I wasn't going to go party with them. Ever. Instead, I invited them to have a 'quiet' drink at a bar at the start of the evening and waved them off once they felt like partying in a club, later in the evening. At this point I just went home and played games or watched a movie. I also started seeing friends one-on-one more often, which just worked better.
I started to notice this, by the way, when conversations I was having just seemed to die out all the time. I thought it was down to people not liking me, and not wanting to talk to me. It took me about 10 years to realise that it was because I never asked anyone questions, and people stopped asking me questions because I didn't really return any interest. So pro-tip: ask questions, even if you don't care about the answers. Listening takes a lot less effort than talking, so I just keep a set of questions at the ready ;) It's a bit of a poor man's guide to being social, but it gets you out of awkward situations where you just can't avoid talking to people about stuff you don't care about.
Anyway, long story short is that you're not antisocial, or broken. You're just part of a (larger-than-you-think) group of people for whom social interaction drains energy, instead of recharging it. It's all right!
I was actually in the market for a used ~2010 320i for a while. Make sure to get any BMW checked by an independent party beforehand, and be prepared to dish out a ton on maintenance regardless of the state of the car. It's just expensive to maintain, so if you're not ready for that - don't do it!
On the specific model: if it's around ~2007-2010 you might run into the dreaded HPFP (High Pressure Fuel Pump) issues with the N54 engines. There are a bunch of stories on this all over the web, but the general consensus seems to be that it might be best to avoid this model of engines unless you get some form of extended warranty.
@frostyryan: nearly everyone is positive about the emotional storytelling in Brothers, but some people had a very frustrating time with the controls. That's what I'm referring to, as it somehow took me zero effort due to odd-brainness.