AIBU to grieve the life I feel I might have had?

It all hinges on acceptance. Accept the fact the you had the upbringing you had. It wasn't right or fair but it's happened. No one ever gets a do-over in life and no one can change the past as much as one might like to. What you can control is today and the choices you make in the future. Find something else to focus on. Friends, career, hobbies, sport, nature.
It won't happen overnight and it sounds contrite when you're in a pit of despair but it really does help to be grateful for the things you do have. Even if it's just a decent cup of coffee or the sound of bird song. Eventually your brain will refocus on the good in life. I've had similar experiences to you and I'm in a better place mentally now by focusing on the small joys in life. I typed my experience in my previous comment but not got the energy to rehash it now.

Start making little positive changes in your life and little achievements and you can feel proud of something that you worked towards.

Are you on antidepressants? I found they help me find an even keel emotionally and mentally, and I can cope with life's challenges better. Without them I fall straight into doom and gloom. I've accepted that they are part of my medical needs now. I know they're not for everyone, just thought I'd mention it.

Fwiw you sound like you had a tough start in life but have made the most of what you could. On paper your current life sounds good but I'm sorry that you're feeling the way you are. I do hope things get better for you.

Everyone is being kind and supportive, but trying to give you much needed perspective. If you just want an echo chamber there is always chatGPT.

40 is still really young. You can retrain, meet a new partner and have many years together. I’m sure you have loads of transferable skills.
im in my mid 50s and I’ve def made stupid decisions along the way and came to regret them, but we have to get on with the life we have and make the best of it (and I’m really not an optimist, I’ve had a lot of health issues in the past two years but what’s the alternative really?).

I want advice about changing my mindset because I can’t change my circumstances. I’ve been very very clear about that.

The circumstances you can't change at all are the ones that have happened. The current circumstances you can most likely change a bit, and the future quite a lot.

Why don't you give us specifics of what you want to change. Just being 20 years younger and rich and fortunate isn't really a very realistic or well-drawn goal. What deep down is it you hanker for?

Also OP it's unfair, no doubt about it and I'm sorry you went through that. People will say all sorts of nonsense like everyone has problems, struggles etc and it shouldn't hold you back but in reality it seems so rare for anyone to do well from upbringing like yours.

I barely ever see it being surrounded by privileged by people, although of course not everything is as it seems with really high achievers but stuff like married parents, grammar school, encouragement etc is definitely the norm and people have their own set of issues.

You aren't in the best place for kind advice, AIBU will give you tough love at best and sheer nastiness at worst.

You can't change the past. Don't compare yourself to others, you don't know what crap they've got going on behind the scenes.
Could you identify one thing that you would like to improve for the future and maybe build on that, rather that trying for a whole life style change? I usually raise an eyebrow at so called life coaches, but maybe someone like that might be helpful rather than therapy, or there are career advice coaches.

I want advice about changing my mindset because I can’t change my circumstances. I’ve been very very clear about that.

And many posters have urged you to get therapy.

If I told you the contents of the email my mentally ill, (absent for all but the first eight years of my life) father sent me in his last communication to me you would have a sharp intake of breath. I’ve only ever told three people. I cried for three days. I never was able to speak to him again.

My step-father went to a top public school and ended up in prison.

I moved out due to the above a-hole of step father into a bedsit at 18.

i have not let one of these things define me. Many people here have had horrific things happen and have not let it define them.

Your experiences are not much worse than some of these here, some would say better, but the difference is that you cannot separate yourself from your early years. You need professional therapy.

judging your entire worth by some rich people you let on holiday who are in the easy stage of life and some fortunate friends is just a recipe to make yourself really unhappy.

Of course you can grieve.

But you didn't come asking about grief - and I think maybe that is what you are really wanting to ask, which is fine.

You came asking how to stop feeling like this, and quite a few of us are genuinely trying to help.

No one is saying that at all - but you are the one playing the ‘I’ve had it harder than anyone else card’, by which you are being dismissive and insensitive to everyone else. We are just saying that sad as that is, as awful as many of our life experiences are, we all move on. And that envying other people and longing for a fantasy life that you think those other people have is a pointless exercise. Because they don’t have that life any more than you do.

I don't want to try and take this over but this resonated with me.

Parents split very young, was clearly unwanted by father with alcohol issues as a young child, my mother was unemployed most my life and there were with food, heating, showering etc because benefits were being spent inappropriately. I can also recall briefly carrying a knife in home for self defence, pointless arguments about absolutely nothing and wanting to take my own life a lot.

I presume this resulted in social skills being really poorly developed and I got picked on a lot, I also had behavioural issues at school and was suspended a lot/got mediocre grades. It was only at A-level when I started getting a bit more confidence in myself and finished with all A* grades which was by far the best at the school but I never had the confidence to apply to any top unis and when I was at uni while I did very well academically I was too much of a wreck to get anything out of it.

I'm now in my late twenties, earn £800k or so from own business, have normal social skills, friends, hobbies etc and even now when childhood/uni comes up I feel really bitter despite doing really well now. Like my childhood and education was just stolen away from me and there's never a second chance plus of course I don't have any close family now.

But sadly Op you can't do that trade.

And in direct answer to your question "how do I stop feeling like this?" I would say you stop feeling like it by focusing on the things you CAN change. That is the only real answer because focusing on what you cannot change will lead to ... well, the fact you cannot change it.

You have scope to change things beyond the scope many people have. You are free to put your needs first, devoid of any responsibilities beyond that. You also have intelligence. You are already leagues ahead of many 40 year olds in terms of possibility just on those two, single facts.

Honestly, I don’t think you want advice. And I’m saying that with kindness. You’re determined to refute every suggestion made here, and you’re creating your own narrative from a lot of the posts.

You're asking for something you can’t have - you’re wishing for a life you’ll never have, and you need to seek some professional support to help you overcome that, accepting your past (which doesn’t mean being grateful for it) and identifying how you can appreciate the things you do have in your life.

@OnceMoreIntoTheBreachDearFriends my sisters and I experienced similar - only when the suicide threats didn’t work, the parent would substitute their wrist for one of my siblings’. There there was the time my step dad insist that I take note what happens to women who behave like whores and proceeded to beat up and rape my mother. I was 8.

Then there was a cousin who witnessed their Iranian grandfather being stabbed by 3 white youths in N London.

Or the neighbour’s who watched not only one son die of a brain-tumour, but the next develop non Hodgson’s Lymphoma, while the mother herself dealt with both her and her sister’s brain cancer diagnosis and mastectomy?

Honestly - however bad you think your life has been, there are LOTS of people who have had similarly harrowing experiences. And worse.

Life can be a bit shit. You can choose to buckle under it, or you get up fighting. It’s the human condition, I’m afraid.

Totes ok to grieve for it, but you need to set yourself a time limit on that and move forward. You’re 40 not 80 - you hsve a level of stability, you have no dependents. You are free to storyboard the life you want and work towards it. You can’t have the time that’s gone, of course, but you can have a brighter future. Build it for yourself, don’t get involved with anyone else until you have made yourself proud of you. Do an actual board of your dreams and start to work out how to make it happen.

But Op you are not even responding to those of us making suggestions.

You are focusing on the comments about other people having it worse.

If it makes you feel better, my life has not been as unfortunate as yours. It has not been perfect, but better so far, much better. Does that help? I thought not ...

Additionally, you seem to think that only academic ability and a good childhood/support system are needed to achieve wondrous things. But that’s not true - intelligence and support often need to be accompanied by courage, emotional intelligence, patience, enjoyment of risk, drive, adaptability, resilience, far vision. Maybe you were gifted in the brains department but would have fallen short because you lack some of these other traits. So there’s no point mourning what might not even have been if you had a perfect childhood. Put the jealousy and grief to bed, accept you’ve done the best you could with the hand you were dealt.

There is so much good advice here.

If it isn’t landing and you’ve had a complex MH history then you probably need a qualified professional. I say that with kindness.

You may lack empathy for others, as someone posted a horrific story of their personal loss above and you seemed annoyed at your attention being drawn to it.

No, I’m saying it’s pointless to compare because you haven’t no clue what someone you know will deal with in the future.

I lost a childhood friend to cancer at 42. In 6 months she went from healthy to gone and had to say goodbye to her 12 yo daughter.

By her own words she had an amazing life. She suffered greatly in those 6 months though and I can’t imagine her sorrow leaving her daughter behind.

I’ve had hard things in life but I can’t imagine how she felt. Her death will always be a reminder to me that life changes in a second. No one is guaranteed a happy healthy life.

You want to know how to move past this? You will have to face your anger and sorrow and disappointments.

Accept that life wasn’t what you’d hoped for and then focus on other things. Focus on the things you are thankful for. Focus on the changes you can make today that future you will be thankful for. Focus on helping others however you are able.

Focus on looking forward instead of looking backwards.

It will slowly become a habit to find the good and once you do you’ll see it everywhere.

You can feel aggrieved - most people here have acknowledged that harm has been done to you. But you’re using it as a stick to beat yourself (and everyone else with). Rather than going ‘look what I have IN SPITE of everything that happened’ … you’re saying ‘everything I have means nothing because I should have had more’

youre entitled to feel that, but it isn’t helpful. And that’s the advice people are giving you.