1.You shouldn't bite the hand that feeds you.
你不应该恩将仇报。
bite the hand that feeds one:
(idiomatic) To cause harm to a benefactor.
2.I noticed she didn't send me a card. I think it was tit for tat because I forgot her birthday last year.
我发现她没有给我寄贺卡。我想她这是以牙还牙，因为去年我忘了她的生日。
tit for tat:
(idiomatic) equivalent retribution, an eye for an eye, returning exactly what one gets.
3.The husband and wife finally cleared the air.
丈夫和妻子最后消除了误会。
clear the air:
To assuage a hostile situation.