I don't really have any advice for you but your post made me reflect on my own experiences, so I'm just going to share and maybe it will help? Anyway.
When I was younger my elder sister was always the golden child... she got good grades, she was good at having friends, she was an amazing dancer, she was always active, her health was better than mine. To my parents I"m sure I came off as fat, lazy, too introverted for my own good, an underachiever. My dad has always been really distant and never really connected with me, and my mom was really busy with my sister's dancing, so as a kid I was left on my own a lot. I didn't have friends in the neighbourhood. I would anxiously wait for my parents to get home, to the extent that whenever a car went by outside I'd rush to see if they were back. There was eventually a turning point where I figured out how to entertain myself (i.e. by playing computer games all day) and started dreading their return because then there would be people around and I"d be forced to interact with them. To clarify, there's no way in hell I was neglected or anything like that, I've been very privileged. But I was alone an awful lot, and combined with the fact that I never did get on well with other kids (and the ones I did click with seemed to always be moving away), I wound up feeling very alienated and unable to communicate with anyone about anything until very recently.
In particular during my A-levels (16-17 years old) I was going through a lot of things, I was super depressed and self harming. I don't know what happened. My dad, of course, only saw that I was not performing well at school and that was his main concern. My mom - I have no idea. She knew something was wrong but we never communicated. I didn't know how to handle it - how could I? And I think she was feeling overwhelmed about my situation, too. I had some bad health problems at the time, too, which meant I went from chubby to nearly emaciated. It's not like they didn't love me, there was just this huge dead zone where nobody was communicating with anyone else, nobody knew what was going on, and nothing got dealt with in the rush to just get on with everyday life.
I don't know... it's all very confusing.