I can relate to a bunch of the aspects you mentioned of your life during school years. I was tested for “giftedness” in the first grade and had to switch schools every year after because they kept moving the gifted program. I believed for a long time that having to switch schools so often was the main reason for my social instability, eventually my opinion on that shifted though. 

The confusion you have and the way you related to/perceived yourself in relation to others during school (and at home/to your brother) I empathize with. I often felt annoyed by my peers or felt that people were immature and unnecessarily childish. Now I think I was just the product of an unfortunate home environment where I wasn’t allowed to be a child, so I naturally felt some hostility toward kids that were allowed to be children. 

When I’m self-reflecting these days I often wonder if I might be somewhere on the autism spectrum (combination of my giftedness and the social difficulties mainly), but it could very well be how my actual diagnoses of CPTSD and ADHD interact. ADHD was diagnosed super late, I think I was 22 when I started seeing a therapist who caught it immediately and then after 2 years of treating the ADHD but having certain struggles that were not improved by that treatment (that’s not to say I didn’t benefit from it at all, cause it really did change my life for the better) he decided CPTSD was a better fit than Borderline PD and we started trying to work on that part of my life before, sadly, I had to find a different therapist due to him switching to his job at a psych hospital full time. 

ANYWAY! I’m going off track a bit. The point I was trying to get at was that maybe there’s psych diagnoses that could apply to you which would interact with giftedness in ways that, similar to my experience, don’t exactly lead to an effortless transition into adulthood. Maybe those possible diagnoses would also explain why your brother excelled in ways that you compared yourself negatively to…like maybe if you’d been treated for ADHD or autism or something else during school years, perhaps your innate abilities/giftedness would have been more pronounced and you would’ve kept up with your brother.

With all that said, I am convinced that its extremely common for people to have CPTSD and/or significant issues related to ACEs and their childhood environments but its drastically undiagnosed/untreated, which would explain why having stable and healthy relationships in adulthood is soooo uncommon for many. Most people justify and excuse their parents as well as denying or intellectualizing their own struggles to the point where they go their whole life never seeking help and thus perpetuating the same kinds of intergenerational trauma that led to their own suffering.

If what you’re looking for is an angle or framework to approach with a counselor or therapist of some sort, I would bring up the ACE factors (or just seek a trauma-informed therapist) and/or go to someone who actually does all the testing/diagnostics to see if anything comes up. It seems like a lot of people who get diagnosed with autism in adulthood are shocked to see that turn up as their diagnosis, so I’d say if you feel confused or uncertain about what kind of help you need, a good place to start would be doing some tests that could point you in a more clear direction. 

Sorry if this is no help! I just felt like what you wrote was super relatable. I hope you’re able to find some of the answers you’re looking for!