Sara Leal told The Sun that Kunis should not trust the actor, after he was alleged to have had a fling behind his ex-wife's back.
Leal said: "Once a cheater, always a cheater. If I were Mila I'd be careful, he doesn't have the best track record. But she's obviously willing to take that risk.
"If I was dating a guy that had cheated on his wife I would be a little suspicious. It would probably make me extra crazy and extra insecure. I'd definitely keep an eye out.
"That would be a red flag in my eyes, if I was dating somebody that cheated on their wife."
Kutcher met Leal and had sex with her in a San Diego hotel room in September 2011. Leal claims that he said he was "separated" when asked if he was married.
Moore confirmed their separation in November of that year, with Kutcher filing for divorce in December 2012.
Leal continued: "I would hate for Mila to have the same experience as Demi. I wouldn't wish that on anyone.
"I would just hope that she's secure, and she seems a really smart girl. Everyone's relationship is different so hopefully Ashton won't cheat on her. Hopefully he learned his lesson."
She added: "I'm sorry about what happened. I'm sorry to Demi - that's a terrible situation and I'm sure it was really hard. It was never my intention, but that doesn't make it OK.
"I've been cheated on so I know how terrible that feels. I can't even imagine what it feels like to be cheated on by a husband and have it blow up in your face.
"My intention wasn't to go out and ruin a marriage. I think Demi handled it in the best way she possibly could."
Recent reports suggested that Moore is still struggling with Kutcher's relationship with Kunis.