Hi OP
'Life is unfair' is one of its fundamental tenets. I've felt the same this past year as have dealt with a terminally ill mother and marriage problems. My list has gone:
It's not fair that my mum is ill and for so long.
It's not fair that I'm having marriage problems.
It's not fair that I am losing my job in six months.
The problem with this line of thinking is that life simply ISN'T fair, and by getting stuck in it's not fair, you start to feel and behave like a victim which only ensures that things get WORSE. Being a victim is a state of powerlessness. You need to feel powerful. As unfair or hard as things are, they CAN change. There is always something you can do to improve your situation, rather than lamenting that it simply isn't fair.
Try reframing it like so:
Its not fair I couldn't have kids till so late in my life.
I wish I could have had my kids sooner, but I am grateful that I do have my kids and that they are happy and healthy. Maybe I had kids later so I had more to teach them.
Its not fair dh lost his job.
I am grateful that DH and I are sticking together through these hard times. He will get another job. Maybe there are small things I can do to help him.
Its not fair I had an abusive family.
I am glad that I have turned out so well despite having an abusive family. My family were not perfect and were unhealthy but did the best they could given their own problems. I have my own family now and can make better choices.
Its not fair I have mental health problems.
I can do my best to improve my mental health. Examples include setting myself small daily goals, going for short walks, getting therapy if required, posting on mumsnet for advice, a short meditation daily, counting three things I am grateful for each day. I can take control of my mental health as much as I can. I am doing well for someone with these struggles.
Its not fair I'm always skint.
I can find a source of income or be more cautious about my spending. I can stop looking as aspirational Instagram pages or social media so as to stop comparing/living beyond my means. Slowly but surely I can build myself back financially to a place I feel comfortable with.
Its not fair I live in a dump.
I am grateful that I have a safe and warm place to live with people I love.
Also remember that lots of people have been dealt very unfair cards. J K Rowling, author of the HP books was a single mother living on welfare who escaped a violent ex and suffered depression when her mother died. She went on to be published and become a millionaire, remarried and had more children. Not every example is so extreme in its rags to riches, but it shows that life can turn around.
The best thing you can do is not give up on yourself or family because things are unfair. You never know when things can change and you have more power/control to change things than you might believe. If you've had an abusive start and have mental health struggles, then you are stronger than you realise. No life isn't fair, but it can still be good!