I share some things about the past trauma with my S/O. But other things I can't share. In fact, I almost wish I would not have even shared them with my T looking back on that. But I had to at the time. I think people are impacted by what we tell them. They see us in a different light. I don't think anyone does this intentionally, but it still happens.
I think it is a very difficult choice to bring in anyone else on such personal things.