OP if you are still reading, no you are DNU to be upset at what might have been. If your future glitters, and I hope it does, your regrets will still be valid. And I agree with previous posters who likened the situation to grieving.
As it happens, I have no living close blood relatives at all and had an “interesting” upbringing, so I understand how it is, to feel apart from pretty nearly everyone else on the planet, even when it’s not strictly true.
In my case my DH has a large family and so my DC have not lost out, but there are only photos of my relatives and no stories to flesh out that hinterland, and at times I feel alone, as if I have borrowed a family, that I don’t deserve.
I’m telling you this because I finally went for counselling around 18 months ago, and one of the themes the therapist picked up was how I set myself rules. Ridiculous made up rules. Rules about how I couldn’t do this or mustn’t do that, at least not before doing something else. The therapist made me realise that the restrictions I put upon myself were artificial, and that I didn’t have to do anything I didn’t want to.
I can “hear” similar rules as you write. You say you can’t give up a miserable volunteer role because it’s needed? Give yourself permission to stop. You are bubbly? Give yourself permission to be miserable. Next time someone says how are you? be honest, or at the very least don’t lie. You don’t like lonely Sundays? Give yourself permission to do something you would enjoy that would make you less lonely. And lovely, get yourself to a counsellor. Work through your head with a professional and see where it leads you. I hope it’s a brighter future 