I would be surprised if Tom had never had any extramarital affairs.

Tom's wife had an extramarital affair.

Sami had an extramarital affair.

He has never had extramarital relations.

Sami's birth resulted from an extramarital affair.

Tom had been having a secret extramarital affair, alternating between two women for the past six months.

Tom had an extramarital affair.

Are you involved in an extramarital affair?" "That's ridiculous."