She's having an illicit affair.

她有一个不道德的丑事。

youdao

A cheap, illicit affair with the woman you love?

廉价的、违法的韵事，跟一个你“爱”的女人。

youdao

Moderately overweight men: 19 percent would consider an illicit affair.

略有超重的男人；19%的男人会考虑风流韵事。

youdao

He got into an illicit affair, and he tried like everybody else to cover it up.

CNN: Sen. Ernest Hollings' closed-door impeachment statement

Burns claimed he was having an illicit affair with the woman for months, behind her lover's back.

BBC: Man jailed for raping woman in Kirkcaldy park

In the same month Taliban fighters publicly flogged and executed a pregnant Afghan widow in the Baghdis area, after accusing her of an illicit affair.

BBC: Summary amputations: Taliban justice in Afghanistan