affair(RELATIONSHIP)
They claimed that she engaged in an extramarital affair with her husband's business partner.
The paper claimed that the policitican had a series of extramarital affairs.
He denied having an extramarital affair with his former employee.

SMART Vocabulary: related words and phrases

Relationships: infidelity
adulterer
adulterous
adultery
affair
bigamous
bigamously
cuckold
extramarital
faithless
faithlessly
faithlessness
infidelity
mess around with something
on the sideidiom
play around
roam
screw
unfaithful
unfaithfulness
wander