Adulterous refers to someone who engages in extramarital affairs or sexual relations with someone other than their spouse. It is often used to describe a person's behavior as being unfaithful, disloyal or deceitful towards their partner.
I mean we're still stoning adulterous women in some parts of the world. (nakedpastor.com)
The Online is perhaps the best position looking for married women who are looking for adulterous relationship. (datingintimate.com)
That certainly seems to be occurring — between 1991 and 2006, the numbers of adulterous wives under 30 increased by 20 percent; it was 45 percent for the hubbies. (omgchronicles.vickilarson.com)