go back on one's word食言
He never goes back on his word.
他從不食言。
He would rather die than go back on his friends.
他寧死也不出賣自己的朋友。
A:Something must be wrong with Bob recently.
最近Bob有點不太對勁。
B:Yeah,he's in a bad mood,coz some of his friends have gone back on him.
是的,他心情不好,因為他的一些朋友背叛了他。