Fetching details from the dictionary...

to betray; to turn traitor (to); to double-cross; to go back on; to be unfaithful (to)
to disappoint; to let down
彼は友人を裏切ってしまった。
He ended up betraying his friend.
期待を裏切らないでください。
Please don't betray our expectations.
信頼を裏切る行為は許せない。
I can't forgive acts that betray trust.