Why do I hate myself so much? Like so so much?

I’ve been socially isolated pretty much my entire life until recently, mainly by choice but also because of homeschooling and constant moving. Now that I’ve started trying to find friends and even romantic partners I’ve seemed to awaken a part of me I had buried that feels incredibly sorry for everything and anything I do.

I’ve named this very unintegrated part of me Sophia and she’s only spoken a few times, repeating that either she’s incredibly sorry over and over again or that she really really wants me to kill myself because she’s in so much pain. Kinda eerie. (She's also not thrilled that I'm telling you this but she's hopeful you might care. But she's really apologetical that she has that expectation of you possibly caring and hates that I'm telling you how she's feeling.)

I think she’s been hiding all this time but because she’s my social part and the part that wants to connect with people I need her to make friends. She doesn’t really see a difference between friends, romantic partners, etc she wants as much attachment and affection as she can. The problem is she’s terrified to ask or initiate any connection and gets painfully insecure and envious of others who express it to each other to the point where being around co-workers or people is torturous 80% of the time.

It’s also worth mentioning that my lifestyle and perceptions are so far removed from anyone else I’ve met, making it difficult to relate or connect with most people. For example, I manage and interact with subpersonalities by personifying them as a cast of 50+ archetypes like Sophia. The initial reason I personified Sophia was to show affection towards her, sit with her in her emotion, and cuddle with her.

I'm quite intelligent and spent 30 hours analyzing my journals with timelines and even interpreting multiple parallel stories I had written years ago subconsciously depicting the suppression of the Sophia archetypes- but got damn I can't figure out what happened.

I’m 19M and have seen counselors, therapists, and psychiatrists for this and many other less intrusive anomalies, none of who offered much help. I don’t understand where this apologetic part of me originated from, does anyone here know?

My friend and I are also apologetic. My friend says hers is because she was forced to apologize for what was not her intention happening as a child. I don't know where mine came from but I've also experienced the same thing as a child.
Was your family perhaps too harsh on you, or did you ever had a kid bullying you despite being homeschooled?

I can relate to your struggle with excessive apologizing. When professionals don't seem to have the solutions we need, it can be disheartening. Even if I don't have an answer, I can suggest you keep on your path of self-discovery. Keep exploring this with therapists specializing in cognitive-behavioral therapy (CBT) or dialectical behavior therapy (DBT) as they often focus on changing such patterns. Also, consider mindfulness techniques to become more aware of when and why you apologize excessively.

This seems like something that trained professionals and you yourself could probably answer better (given you know yourself better than anyone else), but in my experience 'over apologizing' appears to stem from insecurity and the need to be liked.
I think it's healthier to expect that some people won't like you in life - sometimes for reasons completely out of your control. And it's healthier to treat yourself kindly and have a good sense of yourself (without treading into narcisist terriroty). So, Sophia may come from deep insecurities or a deep need to connect with others and have them like you, or both, or all that and more.

Also, personally, I wouldn't go too deep into over analyzing yourself or subpersonalities. For the overly introspective types, sometimes it's better not to overthink things and just let yourself be. Things will never be perfect and you can't wait for everything to be 'right' to be happy and let yourself live.
I have a strong feeling if you allow yourself to be your genuine self, and let go of insecurities, that connections with others will come easier than you might think, but you'll have to put yourself out there to make it happen too (ie. picking up a hobby, etc)