1. His wife cheated on him; that’s why they got divorced.2. She was having an affair with a married man.
 cheat on somebody have an affair這是最普遍的說法.
他太太有外遇, 所以他們才離婚. 她與有婦之夫外遇.< >
老師 (讓小朋友出校車後): 別嬉戲，別跟陌生人說話。 (請填空)
Teacher (after letting kids out of the school bus on a field trip): No horsepay. Don't talk to strangers.