Do you still remember how you were?

Yes, though the painfulness of the memory is fading.

I've also experienced "calculating" social situations, emulating alien behaviors - and then later finding them to have become natural and enjoyable.

Do you have a particular example? For me, one of them is smalltalk. I don't necessarily enjoy all smalltalk all the time, but I enjoy it a lot more than I ever thought that I would, back when I viewed it as "pointless" and "meaningless" (because I didn't understand that the purpose of most social communication is to share emotions, not to share interesting factual information and theories). Similar story with flirting.

With such social behaviors, everyone "learned" them at some point. Most people just learned them during their formative experiences. Some people, due to a combination of biological and social factors, learn this stuff later, or not at all. The cruel thing is that once you fall off the train, it's harder and harder to get back on. See the diagram here for a graphic illustration.

For the past few years, I've just been coasting - I haven't changed much and I don't know how to summon up the drive I had before.

I've gone through periods of growth, and periods of plateaus. Once I got to a certain level of slightly above average social skills, it became easy to get complacent with mediocrity. I start making progress again when I keep trying new things, going new places, and focusing on what on what I want.