I give people a chance and if they betray me I never ever feel the same way about them ever again.
If its trust over something not that important I just move on and am civil to them, but if they betray me on a very personal level then I can simply forget they exist and sever all feelings and attachment.
They are simply dead to me.
Most only get one chance with me, some get two, fortunately I am lucky in that I can see right through most people and assess whether I will let them get to know me or not, or just get the full of bollox version.
I think most people do this, I am just the same as everyone else.