what's done cannot be undone 覆水难收；生米煮成熟饭

【例句】
But we can't change him, so we must make the best of it. What's done cannot be undone, on use crying over spilt milk.
我们不可能改变他，故而必须尽量处理好。覆水难收，后悔是没用的。

I take anything to save, when loves what is done cannot be undone, who can bless who, did the wish wait for who.
我拿什么拯救，当爱覆水难收，谁能把谁保佑，心愿为谁等待。