小三的出现，必然伴随着一方的“劈腿”，或者说“出轨”，可以用以下两个英文短语来表达

1. Have an affair with sb.

eg. He is having an affair.

他有外遇了。

2. Cheat on sb.

eg. Does he cheat on his wife?

他是不是出轨了?

咳咳来正经的啦

confront

1、面对，必须处理(问题、任务、困难等)【近face】 But not even a great health care system can cure death—and our failure to confront that reality now threatens this greatness of ours. (2003 Text 4)但是即使伟大的医疗卫生体系，也不能治愈死亡——而我们不能正视这个现实却正危及着我们医疗体系的伟大。And it's time we reprioritize resources to confront this new reality.(Chicago Tribune)是时候将资源放到优先位置来应对新的形势了。

2、对峙，对抗，遭遇：

the interaction and confrontation between shared and competing beliefs about the science and the technology involved (2012 Text 3)与该科技相容或相抗的理念会相互作用、相互对抗(confrontation 是confront的名词形式)...as one clergyman learned in confronting folk along the coast who mocked that they had not come to the New World for religion.(2009 Text 4)……正如一名牧师在与沿海地区渔民相遇时所了解到的：他们嘲弄地说来新大陆不是为了宗教。