That's a really good question. Hmmmmm.
I agree with Dave that a good starting point to gauge it is how much do you think your carer can handle. That said, I think the nature of the trauma plays a huge role in that.
For example, my "PTSD-inducing trauma" (not sure quite how to put that) was a severe bite from my husband's Akita. I tend to be vague about the dogbite unless I have to in order to get a point across, because it was my husband's dog and the whole situation is very emotionally charged for him. I know he feels bad/guilty/responsible when I talk about it, so I try to avoid being detailed.
However, when it comes to a lot of my childhood psychological/emotional trauma, I will discuss it with him because he's really good at seeing it in a way I don't...almost like a therapist. He's helped me explain a lot of my own responses and put them into proper perspective. It also has helped him gain perspective in understanding my behavior and the way I think.
Another good question to ask might be, "What is the potential backlash/consequence of talking about this with my partner?" In my case, my husband will no longer allow either of my parents at our house, and wants nothing to do with them. I'm good with that, but some people might not be. Personally, I would not be comfortable sharing details of sexual abuse with my DH (don't remember anyway). To me, that has the potential to cast me in a light I wouldn't want to be in with him.
I do think some information could ruin or destroy a relationship if it causes the carer to perceive the sufferer in a way that would negatively impact the relationship. For example, if the trauma would be what your carer sees when they look at you, things could go downhill very rapidly. Again, that goes back to what Cragger said about how much can your carer handle.
Sorry, I'm not explaining myself very well tonight. :crazy: