My parents cut us off from maternal extended family when I was 10.. they had cut us off from paternal extended family when my mother was pregnant with me and they had moved to the other side of the world, even though my father knew his father was dying of cancer. My paternal grandmother blamed my mother - she thought my mother knew - and the truth of the situation only came out when my father left my mother when I was 21. We saw my paternal grandmother once after he left...she lived another 30 years and we never saw her or any of my father's family again.
My parents made some very stupid decisions when I was 10, my mother's family made their opinions (entirely valid) known, and so my parents cut them off too. My mother was one of 9, so a very large family...we'd been very close to all of them up to that point. My parents actually made our family 'disappear' for 7 years, for most of the 80s. My whole childhood my parents strongly discouraged myself and my brothers from having hobbies, friends, outside interests etc Contact with my mother's family was only resumed when my younger brother got drunk on his 18th birthday and rang my grandmother. My father left my mother 6 months after that for the woman he'd been having an affair (one of many he'd had their whole marriage) for a year. My mother ended up going back to our home country (on her own), did reconcile somewhat with her family but the damage was never really repaired and they never totally forgot or forgave...particularly as my mother never actually apologised for any of it. She is now the oldest of the last 3 siblings left, and her younger sister is terminally ill with cancer.
None of the above is my fault. Like others have posted, I've found, particularly in the last 20 years, that most people are only there for the good times, and the pandemic has made that even more true. I consider myself lucky to have one good friend, but have only seen him once in the last year as he has health anxiety made worse due to covid and is still petrified of catching it, so won't socialise.
My whole childhood was toxic, chaotic and stressful. I'm 53, being treated for C-PTSD, on top of being bipolar. I was in a car accident when I was 17 and my physical disability now means I can no longer work....I haven't worked full time in 7 years. I now have no family in the UK, I'm not on good terms with my mother and haven't seen her in 13 years. My partner of 12 years lives 200 miles away for work and I see him on average once a month for about 5 days. During the lockdowns I went a total of 15 months without seeing anyone but delivery drivers and the postman.
I'm also lucky that I like being on my own and only rarely feel 'lonely'...but when I do, I'm sad that decisions that were made when I was a child are still having an effect 40 years later.