How can you regain trust in your best friend when they have lied to you they know you know but won't confront the issue?
First, they are not your best friend if they lied to you and
won't admit it. It is up to them to prove themselves to you. It
takes a long time for someone to rebuild trust after they have
broken it. Ask yourself this, if they lied to you once, how do you
ever know they are telling the truth or when they will lie
again.