Anthea Turner says she monitored her ex-husband's satnav and tracked his bike rides when she suspected he was being unfaithful.
The TV presenter (56) was married to Grant Bovey until 2015, when she was granted a divorce on the grounds of his adultery.
The couple split up in 2012 but briefly reconciled before separating for good in 2013.
Turner said she grew suspicious when Bovey became angry after she told journalists she was happy about the reconciliation.
"Instead of sharing my happiness, he went ballistic," she said, adding she started checking his emails to see if he had been where he said he was, before checking his car's satnav.
"All of a sudden, he began announcing plans to cycle to all sorts of strange places."
Turner has written a book, How To Survive A Divorce, for women going through similar situations.