What do you do when you have a feeling that someone is untrue?

Get to the root.  Ask yourself why continually until you get to the root cause and you can no longer ask yourself  why.

Has he/she done something to make them unworthy of your trust?

How much does that matter?

(I sometimes like to draw this all out)

I trust emotions,  they are what you feel is real.  Dismissing them will only lead you to a negative feedback loop.  DEAL with it, ACT on it by telling the truth of how you feel.  Otherwise, you unknowingly enter into a strange arrangement were you play detective & its a righteous game of who's being wronged.  Its all bad.  The truth is within yourself.  The question you should be asking is:

Are you honestly ready to trust this person? No if's, and's or but's.

And if in reality he or she is being truthful.  What will it matter if you don't believe him or her?

Feelings & emotions get convoluted. Period.  It would be nice to hear the truth, get absolution, closure.  But you're not always going to get it no matter how you manipulate the situation.  Seconds, minutes, days, sleepless nights add up.  You're only getting your heart broken by little minute fractures at a time. 

When do you want to remove the blinders & see what is really happening & what you do have control over? 

Feel what you feel, whether that be mad, sad, used & abused.  But get over it & don't dwell, love.  Don't waste the pretty or handsome because you get uglier & uglier (inside/out), when you are unhappy.

And there's your soul-tion.