1To deceive or turn against someone who trusts you, such as a friend, ally, or comrade.
彼は仲間を裏切って敵に情報を売った。
He betrayed his comrades and sold information to the enemy.
親友に裏切られて、しばらく人を信じられなかった。
After being betrayed by my best friend, I couldn't trust people for a while.
会社の同僚を裏切るような真似はしたくない。
I don't want to do anything that would betray my coworkers.
彼女は約束を破って彼を裏切った。
She broke her promise and betrayed him.
2To turn out differently from what was expected, disappointing someone.
その映画は期待を裏切らない面白さだった。
The movie was every bit as entertaining as we expected, and didn't disappoint.
天気予報が外れて、私たちの計画を裏切った。
The weather forecast was wrong and ruined our plans.
続編の出来は前作の評判を裏切るものだった。
The quality of the sequel let down the reputation of the original.