I’ve been thinking recently about how does one decide -
Who to trust with our story?
Who is deserving of hearing our innermost thoughts and feelings?
Who has earned the right to know us on a deeper, more intimate level?
Who is emotionally mature enough (safe enough) to peel back their layers and ours?
And - when?
I think one can only answer the “Who” questions by answering the “When” question first…over TIME. It takes time to learn who we can trust; and time to re-build trust if it has been broken. Spending time and engaging with your fellow co-housers for example, will let you know who is trustworthy, who is deserving of hearing/sharing innermost feelings, who is willing to earn the right to know us on a deeper level and who is safe enough to peel back our layers with. And, though I wish at times that time would hurry up or slow down, I am reminded that YOU CAN’T PUSH THE RIVER!
I believe as we become more attuned to our body and we get more un-triggered experience with people, we can notice a clearer sense of openness – and not openness. We can feel parts of us give encouragement and other parts might be attuned to warnings.
I go slowly, except when everything really is a YES head to toe.
Then, I will share something deeper. Perhaps even something I haven’t shared with other people I’ve known longer yet who are not as wholly a YES for depth and closeness.
I would not share something that, if they do not handle it well, would cause me harm. Even now there are aspects of my being that are more raw than others. There are also aspects that are so core for me that sharing them and noticing what comes back can give me a LOT of information about how another being is oriented.
I do believe there are certain milestones I’m aware of…
The first time I say NO to something that matters to them. How do they take it?
The first time they say NO (or fail to) about something that matters to me.
The first time we co-create together. And every time thereafter.
Making decisions together, how we find our yes-yes’s.
How we sit and handle with safety and respect a difference in perspective on something happening outside of us.
How we are together when both are dysregulated, or me, or them. What’s the repair process like (assuming there is one).
Those are key ones I sorta “track” in my relationship mind. And none of those aspects were conscious until I started doing the emotional work… and discovering what actually makes relationships thrive together.
One of the ways I do it is to “poke” people and see if they let me in, or quickly change the subject. I might make a vague reference to how I grew up, and see if they respond to that or if they quickly start talking about the weather. Then I know if I can maybe disclose a little more at a later date or if next time I can just nod a polite hello and keep walking. 
I also see how they talk about other people or themselves. Do they overshare intimate details about their own lives, or that of others? A huge red flag for me is when the person I’m talking to is sharing something about another person that is clearly not theirs to share.
I had a friend I excised when she sat down in front of me one day and breathlessly announced that her friend X was really upset because her 12 year old daughter walked in when she was (insert graphic sex act here) with her husband. I felt sick because I knew she was sharing anything and everything I told her as well, with no discerning that some things are to be kept private and confidential.
Whether we’re coming from blind trust or blind distrust, you’ve described here what I’d call the process of discernment.
We test with something that isn’t too deep or too vulnerable. We notice how they are with us, both at first and over time. We see if there’s a sense of knowing (and wanting to be known) by each other mutually… or is it one-sided or not present?
How do they handle intimacies? Can they hold that space, or do they need to “pass it along” – especially inappropriately (as you described in what I’d consider non-consensual sharing of private details someone else trusted them with).
I was someone who tended to trust and be burned. I’m now much more discerning (because to thrive I do need people I can trust in my life). I’m also clearer about what I want kept private.
“I have something about ____ that it would help to share with a trusted friend who can keep it confidential. There’s nothing criminal here, just something I’m feeling embarrassed about and could use some reassurance and a listening heart. Are you in a place where you can keep such a confidence? Is that your nature, or do you prefer not to be told confidences if sharing them with others would be a betrayal?”
Oh, way lots of words there. I hope you get the gist. It comes out better in shorter parts with more step by step confirmation. I’d also – if it is really (!) something I would never want shared – not even ask someone who hadn’t already shown a respect for the private and confidential aspects of what we share together…
I learned that the hard way.
I also feel really good knowing that I do have people who mutually share deeper feelings, ones that may be fleeting yet still respond to being shared rather than banging around inside or eating holes in my heart.