What will you do if you learned that someone you trust isn't honest to you?

I think sometimes you must forgive and forget. Have them your a second chance. Make them feel their guilt of what they have done while forgiving them. Talk to them, maybe they have a valid reason why they do that.

honestly if i learned or know someone that i trust lied to me, oh its a very depressing feeling. I will really talk to that person to make things clear. i will be really bothered and perhaps couldnt sleep well knowing that someone i trust lied to me and yesh its starts in small thing so before it gets big, it must be fix as soon as you know. Confront that someone and have a talk and from there you will know if its true or not.