It takes me a long time to trust someone. I don't think there was any one moment that I realized, "Hey, I trust my T," but there are a few things she's done that have led to my eventual trust:
She has a similar sense of humor to mine.
She can tell when I'm lying to her when I'm too afraid to tell the truth.
She is willing to open up just a little bit about herself so that I can see I'm not weird or bad for feeling a certain way. I understand T's can't share that much about their lives but it's nice just to hear, "I understand that, I feel that way too when _____ happens."
She is kind.
When she listens to me, I feel like she's really listening. I know this is something all (or most) T's do, but it makes me feel good to know that she keeps notes on our sessions and reviews them before I come in so that even if my last appointment was more than a month ago, she remembers what I said to her.

I realized after last week's session, when I lied to her about feeling suicidal, that I'm actually ready to tell her the truth about those feelings. I am looking forward to our next session so we can talk about it.