Stab [stæb] 捅/捅刀子
stab someone in the back 背叛，辜负
He stabbed me in the back by going out with my ex. 他跟我前任约会相当于在背后捅我一刀。
Traitor [ˈtretɚ] 叛徒
You traitor. How could you side with them? 你个叛徒，你怎么能和他们一起？
You’re a traitor. 你是一个叛徒。
Betray [bɪˈtre] 背叛
She betrayed me for the last time. 这是她最后一次背叛我。
Double crossed 两面派
They double crossed me. 他们跟我耍两面派。 / 他们出卖了我。
XX sold XXX down the river 某人背叛某人
He sold me down the river just because they offered him money. 他背叛我，就是因为他们给他钱了。
go back on 背信；背弃；出卖；违约；背叛
He would rather die than go back on his friends。他宁死也不出卖自己的朋友。
two-timing 出轨
He is two-timing his wife with Olivia. 他背着妻子出轨了Olivia.