Melissa Watts was “carted off” by police in front of her young son in the early hours of the morning and kept in custody for several hours while she was fingerprinted and interviewed.
She then spent weeks on bail as police investigated the two notes, in which she was accused of threatening to kill Michael Killick.
But handwriting experts proved Ms Watts’ innocence and Killick, 40, pleaded guilty to perverting the course of justice.
A court was told he had “retaliated” with the letters after Ms Watts posted “very embarrassing, sexual” comments about him on social media after they split.
The jury heard the couple had been in a “difficult” relationship for 20 months, which ended with an alleged assault on Ms Watts.
Jailing him at Maidstone Crown Court, Kent, judge David Griffith-Jones said Killick’s actions were “calculated, vindictive and spiteful”.
Killick, of Shiney Row, County Durham, was given 14 months in jail.