I am desperately trying to write my life story. it is so painful, that it is too difficult.

Don’t do that to yourself. Do what moves you away from pain, not what causes you more. You are not ready to be writing, and revisiting, this pain. Maybe you will be at a later date, or maybe never at all. It’s okay one way or the other. The only way I can get through each day is to not think about certain things. If I did, I’d be literally unable to function. Don’t make the suffering worse than it already is. It’s too much. 🤗

A lot of people journal or keep a diary. Some people, I have heard feel a lot different after writing out their feelings. It may help you, I'm just saying. Perhaps writing it like a novel would help you detach from some of your emotions. I find that sometimes writing things out is therapeutic. If you haven't started yet, thinking about doing it may seem more traumatizing than if you actually start. Once you start you may find a balance. (imho).

Don't try to tackle it all at once. Tell it one story at a time. The good times and the bad, the success and failures. Don't forget the funny stuff, humor is an important part of who a person really is. Start with vignettes, pictures that are a window of who you are. Later you might try to put it all together, but for now just tell a story, one incident at a time. The whole picture will emerge eventually.
We don't eat the whole cow at one sitting. We cook the steak and eat it one bite at a time. It gives us time to digest.

I'm going to live as long as I can and let someone else write my life story 😊

My advice would be to go back to basics and try writting about other people or events first to reaquaint yourself with your writting style, think highschool english class, prose, narrative style etc, meditation may help you relax and find a starting point, if you make this a bucket list item before death, your brain is naturally going to fight you in order to prolong its life.

Start with a summary. These can be chapters of elements of your life, or age breaks, or however you want to describe it. Don't put many details in, just a quick summary. Later you go back and put the details in, when you have the strength to do it.

I have been working on mine a little at a time, not going into too much detail. I got my father to do his, carefully printed on yellow legal paper. I just finished telling about high school, which included the story of how my wife and I met and started dating.

I’ve read authors describe writing a painful autobiography as the best therapy they’ve ever had.

Why do you have to write it, record it.