劈腿的3三种英文说法

have an affair with someone
与某人有暧昧关系,有外遇
She used to have an affair with one of her husband's friends.
她之前和他丈夫的一个朋友搞外遇。

cheat on someone
不忠实于 (配偶或伴侣)
He’s cheating on his wife.
他背着妻子在外面搞外遇。

step out on someone
对伴侣不忠
Hank has been stepping out on Sophia, and she doesn’t know it yet.
Hank一直对Sophia不忠诚，但Sophia还不知道。