I don't think any human can live well in isolation from other humans. Even monks in a monastery are part of a community that is closeknit and that regularly meet for group prayer. I've had a mild social phobia since early childhood. I could echo a lot of what you say, as being true for me. Before considering a diagnosis of ASD, I would look at situational causes because I believe those are more common. Specifically, what kind of social habits did your parents role model? My own parents tended to not mingle a lot. Neither had close friends. They tended to socialize only with blood relatives. Social ease and competency depend on a set of skills that are not innate, but must be learned. We need capable role models. Plus, we need lots of experience.

You are self-conscious in social situations because you feel unsure of what to do. I go through that a lot myself. Regardless of the cause, the fix is to go after and embrace opportunities to interact, knowing that we may be a bit socially clumsy and will make mistakes. Fear of embarrassment can be a strong reason to hang back, which we must push past.

You're very self-aware in a good way. It sounds like you have plenty of empathy. You have found yourself in relationships where you seem to invest more than the other party, and you wonder how to handle that. Me too. I tend to back off and not pursue closeness beyond what the other party seems to want. I don't like to get my feelings hurt by rejection, so I am probably overly quick to back away from others. That sensitivity to rejection probably has a history behind it that reflects the social dynamics we experienced within our nuclear families. I tend to look to "nurture" over "nature" as being what shapes our personalities. To some extent, that's just a prejudice I have. But I have found that knowing family dynamics is sufficient to explain a lot.