How to not feel this way?
Obviously I don’t know you so please take what’s helpful and ignore what isn’t, I’ll certainly be wrong in places.
It sounds to me like your longing for success is the story on top of some very very legitimate feelings about not being wanted, not being enough, not belonging resulting from your difficult childhood and subsequent difficulties socially. Very common for autistic people to feel this way, very common for victims of childhood abuse to feel this way.
children especially but also adults in abusive relationships often internalize any poor treatment of themselves as being deserved. It leads to a deep and profound sense of shame. You may have spent much of your childhood trying to be good enough to deserve loving stable parents. If school was a place where you could do well that would be a comfort to you but could easily become too central in your identity. That aligns with not wanting to risk that identity by eg applying to Oxbridge.
Your brain is trying to protect you. “That’s impossible” or “I won’t try” protects from failure that might hurt something very precious to your psyche. And “I would have / should have” is a similar response to the shame you feel. I think that’s why you find other people sharing stories of adversity so threatening (though I also want to acknowledge that some posts have been genuinely horrible).
I think some posters are trying to suggest radical, total acceptance as one path forward. Don’t try to bargain with the shame, don’t think about what could have been. Life went as it did, you acted as you did. Some people find comfort in a sort of detachment, looking at a memory without indulging or pushing away emotion, just accepting it.
Others suggest focusing forward and on the things you can do and can take control of.
It’s clear that continuing to focus on the negative feelings and narrative so much is harmful to you and keeping you stuck. There’s no blame there, truly. I was once told that depression is addictive, basically because familiarity is addictive. Your brain finds comfort in retreading the same paths, it’s scary to think in a different way. I don’t believe you can force your way out of painful emotions but it is possible to give yourself a break from them by choosing to focus for a while on positives. It sounds glib but it really can help.
Start small. You don’t need to change your whole life to start feeling better. The grief for what could have been is real. Let yourself feel it and then let yourself come back to the present. You did and do deserve to be loved. Life is easier for many, that’s true. It’s also true that you’ve done really well, and it’s healthy to feel proud of achievements that aren’t “exceptional”.
some people find it helpful to imagine the child version of themselves inside their mind. now you’re an adult you have the privilege of talking to that child version of you the way she should have been spoken to by parents. Loving parents are proud of their child’s achievements even if they’re not always top of the class or don’t win an Olympic medal or whatever. When you allow yourself to feel pride in the fact that you’re good at your job, for example, without the caveat that you “ought” to have a better job, it’s like giving your inner child that affirmation she should have had. She deserves that kindness.
the last thing I hear from your posts is the sense of the grind that so many are feeling right now. Life is expensive and well paid jobs are scarce. It’s shit, and very much not a reflection of you. Longing for things to be easier is totally natural. Finding places where you can have agency helps a lot against the sense of being trapped.
well I hope something in there was helpful. You’re obviously very strong, given how much you’ve already come through in life.