The discreet dating platform delved into a survey of 2,000 people and their dating habits pre-and-post-pandemic and found that September knocked January off the top spot because "unhappy people were looking to start afresh."
The pandemic seemingly created a cheating boom, with Illicit Encounters announcing the busiest year in its 19-year history.
Jessica Leoni, sex and relationship expert at the company, said: "Sex-tember is here, which means a surge in affairs.
"It will be even more pronounced this year because working from home is gradually ending, and more of us are returning to the office.
"Affairs always traditionally peaked in January but, while New Year cheating is still really high, autumn is now the peak time for adultery.
"Lots of us get sick of a partner after two weeks away in the sun, and we return to work determined to have some fun with someone new.
"The pandemic has made more of us live for the moment and shake up our lives if things are not working."
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