I think all situations involving trust, come with boundaries......I trust different people in different ways. Even the most trustworthy have their vulnerabilities....and can fail us....a night out on the town and they tell something confidential or embarrassing (you know the ....don't tell, but.....person X told me.....Y....giggle giggle) Boundaries and clear communication, and scoping out how reliable someone is are key things I think to help me effectively assess trust levels in others. Expectations, though......can cause heartache.....so, the fewer expectations I have of others.....the less I think I'll be hurt again....and the better boundaries I establish.....the less leeway there is to be hurt badly.I'm for the most part pretty anti social. But I do have a few people I would call a friends.
Trust is key. If I can't trust you I can't be around you.
Loyalty is anouther big thing. I'd do anything for my friends and even though I don't ask much from my friends but if I ever did I'd expect the same in return.
Kind and caring.
But, I believe people will always disappoint us once in a while.....it is renegotiating and communication which helps to resolve trust issues that haven't gone too awry.