The investigator warned to be on your guard if your partner suddenly takes a new interest in "their appearance and weight".
"Also be aware if they keep buying new clothes, have a new "obsession" with perfume or aftershave, spend more time showering and 'start washing their own clothes'," he continued.
Being "secretive" and taking their phone "everywhere" with them may also be a sign of infidelity.
Others agreed, sharing their own key warning signs, from "Phone face down and with them at all times", to "Coming home different hours of day and night".
Another added, "They say they're going to wash the car at 10.30 at night and don't return for several hours ... my ex."
A psychologist recently told the Daily Mail about a lesser-known secret to spotting a cheating partner.
Daniel Acon suggested analysing what your partner says, rather than their behaviour or expressions. In an Instagram video, he suggested that if your partner accuses you of cheating without any proof, it could be a red flag that they themselves are unfaithful.
"Disclaimer: this only works if you haven't broken their trust, otherwise, they might be justified in how they feel about you," he added.
"If you're dating someone and they start accusing you of cheating or they're worried that you're talking to other people without any evidence, it usually means that they're cheating and talking to other people ... they're just worried that you're doing the same thing.
"People tend to project what's inside of them onto other people."
And while many viewers were "mindblown" by this, others disagreed.
"Not really. What if someone has anxiety and fear of abandonment," one person wrote in the comments.
"What about the trauma of being cheated on?' another asked, to which Acon responded, "Absolutely, I didn't say this was every single time."
Another added, "I have a fear, not because I'm doing it myself but I'm scared to get hurt while I let my protection wall down."
