But still, after all those years, I don't feel bad about it. That's life and life is a mess sometimes. There are things you can change and there are things you can't. And most often a change takes quite a lot of effort or leads to nothing.
You need to distance yourself from this mess. This is easier if you first and foremost take care of yourself. Lead a good life, take care of your family, do sports, do something else than think about your job all the time.
And on the job, just try your best and even if things fail, learn from them and carry on. Hope this helps a bit. Stay strong and all the best to you!