Definitions of betray
to not be loyal to something or someone to which you should be loyal, especially to a country or a person eg by giving away secrets or by helping their enemies
Did her sister betray her to the enemy?
to not do as you promised
The Government has once again betrayed its election promises.
to reveal something about yourself that you have tried to hide or would not want revealed
This is no liberal conspiracy; the president's own words betray his prejudices.