Here are some examples of how it was used:
* "He that is false to his friend, shall be betrayed of his own." (from the *Canterbury Tales* by Chaucer)
* "The kyng was betrayed of his own counseil." (from the *Chronicles of England* by Raphael Holinshed)
The word "betrayen" has undergone some spelling changes over time, eventually becoming "betray" in Modern English.