The ex-Liberty X popstar admitted to having a "drunken" snog in a nightclub, but denied reports that she had an affair with Strictly Come Dancing's Matt Di Angelo.
"I cheated on Andy on holiday in Marbella last year," she told OK!. "It was a snog in a nightclub but Andy's saying that I tried to deny it but that's not true.
"It was on the last night of the holiday and the day I came home I told him. I felt sick with guilt and worry. I won't blame the alcohol but it was stupid and drunken."
When asked about her relationship with Di Angelo, Heaton said: "I didn't sleep with Matt.
"The only thing I did wrong was that I found him really attractive and cute - which woman wouldn't - and as a married woman I shouldn't be thinking this."
The singer also denied rumours that she had relationships with Big Brother 8 contestants Ziggy Lichman and Liam McGough.
Heaton and Scott-Lee, who married in 2006, announced their split last month.