A bit of backstory
My parents are separated and my Dad has a long-term partner who he has been with for over 10 years now. She (my Dad's partner, let's call her Eve) has a close group of friends who she sees on a regular basis. One of Eve's close friends (let's call her Annie) works at the same place as me, in different departments but we occasionally see each other at lunchtime.
Someone in my family, Adam, has a mental health condition which sometimes means the way they behave is not the most polite, can come across as rude etc. I mention this because it has caused issues in the past. Eve has found Adam's behaviour to be 'unacceptable', has told my Dad, who has then told Adam which has caused a lot of grief and loss of trust. I think this goes to demonstrate how sensitive Eve can sometimes be about a person's perceived behaviour, which is why I want to avoid as much as possible any conflict.
Adam had recently been going through a 'down period', whereby I mean their mental health was not in good shape for several reasons. I would talk to my (our) Dad about this when I would see him. Sometimes Eve would be there too, but I felt like there was no reason not to trust her with the information. In essence, Adam was not sure if he wanted to go on a family holiday because he wasn't feeling great, I felt it was important to tell them because they would need to be aware and available had that been the case.
So, on a couple of occasions at work, I have bumped into to Annie at lunchtime and she has asked me about a specific 'event' that either myself or Adam would have discussed with my Dad. My Dad may have discussed this with Eve which I don't see a problem with unless it was explicitly stated to be confidential between my Dad and Adam. I do however take issue with this for several reasons:
The information I shared with them, was shared with confidence that it would be private between those present. It was not explicitly stated but I definitely would expect that to be the case.
I hardly know Annie. She is a lovely person but we are not close and she isn't a close family friend. On the contrary, she is only friends with Eve, not my family and certainly not someone who I would divulge such personal information to.
When Eve and Annie normally see each other it is with a large group of friends. So if Annie knows about this then it is likely that everyone else present at the time also knows. People who I don't even know. And who knows who else could have been told.
As nice as Annie is, and as much as I like her, it is not her (or any of Eve's other friends') business to know the inner workings of my family or Adam's personal information and I need to make sure that Eve doesn't do this sort of thing again.
This has only happened twice. With the example that I mentioned above and with another example.
As mentioned earlier Eve has a tendency to be very sensitive about matters such as these. How can I go about asking her not to share such information? In the meantime, I know that I can refrain from saying anything with her present, but I know that I do need to tell my Dad important things. But then I would have to tell him explicitly not to share this with Eve which raises the same problem.
This is especially important to me because if Adam were to find out about how Eve had been 'spreading his secrets' it would cause a lot of conflicts and unnecessary grief in our family.
How can I make Eve know that she can not be spreading personal family information such as this with strangers?
Thanks for any help.