I can totally relate.

When I feel guilty about not trusting someone who may be sincere, I feel almost rushed to trust.

And when I rush to trust, I start to ruminate on my doubts about this person (ex. "What if she leaks the information I shared with her in confidence?").

So to take the pressure off of myself, I recently decided to remain neutral about people I don't know too well for a while. I decided to say,

"I don't need to make up my mind about this person yet. No one is enforcing a strict deadline on me. I will take my time to get to know this person for at least for the next (x amount of) months. I will not put myself at risk by trusting too soon, but I will also not ruminate on my doubts as it is not healthy or necessary (since I have not taken any risk yet with this person)."

Of course, this is for people that I don't know well. As far for people I know for certain that I cannot trust after many years, I know better now to guard my heart.