I generally have come to see trust less in relationship to others, and more in relationship to myself. If I trust myself, in the event that I feel disappointed in others actions, it isn't the end of the world--simply a mistake in judgment. I give others the opportunity to show me who they are, and then I don't force my expectations/needs onto them under the guise of trust. I guess it's about taking responsibility for my own expectations, and if others don't fulfill them, it's usually because I haven't allowed them to be who they are. Therapy taught me to not walk around with a template in my head, trying to fit others into it as a test of trust. Rather, to trust myself enough to express my wants and needs, allowing others to fulfill them or not. And then deciding if such response is "good enough." And that determination depends upon the degree of the relationship. I expect more of an intimate partner than a friend; more of a friend than a work colleague. And I don't expect any one person to fulfill all my wants/needs. It seems to make it much easier to trust people when I'm also willing to accept them as they are.

ETA: It also allows me to feel far more free in how I fulfill the wants/needs of others. I don't feel compelled or without choice, nor guilty, as I did growing up. And since I give what I give freely, there's no pressure of expectations unfulfilled in return.