To be treacherous to

• sell out
• ?
• double-cross

To disclose in a breach of confidence

• discover
• spill
• unveil
• uncover
• tell
• reveal
• let out
• give away
• expose
• divulge
• blab

To cause to accept what is false, especially by trickery or misrepresentation

• four-flush
• have
• bamboozle
• trick
• take-in
• mislead
• humbug
• hoodwink
• fool
• dupe
• double-cross
• delude
• deceive
• cozen
• bluff
• beguile

To deliver into the hands of an enemy

• turn state's evidence
• cross up
• bite-the-hand-that-feeds-one
• stab-in-the-back
• sell out
• deliver up
• double-cross
• give the Judas kiss to
• play Judas
• sell-down-the-river
• deceive
• disappoint
• let down
• trick
• go over to the enemy
• be disloyal to
• be false-hearted to
• be false to
• break one's promise
• delude
• turn informer
• commit treason
• turn in
• inform against
• inform on
• break faith (with)
• play false

To lead astray

• corrupt
• misguide
• seduce

To reveal

• make-known
• uncover
• disclose
• divulge