(it's/there's) no use crying over spilt milk
It does no good to get upset over a bad decision or unfortunate event that has already come to pass and cannot be changed. We were pretty disappointed to have lost the championship game, but there's no use crying over spilt milk. We just have to train harder for next season! I know you really wanted that job, but you weren't hired, so it's no use crying over spilt milk now. I was such a fool to take out that second mortgage. Oh well, no use crying over spilt milk!
(there's) no point crying over spilt milk
It does no good to get upset over a bad decision or unfortunate event that has already come to pass and cannot be changed. We were pretty disappointed to have lost the championship game, but there's no point crying over spilt milk. We just have to train harder for next season! I was such a fool to take out that second mortgage. Oh well, no point crying over spilt milk!
cry over spilt milk
To be upset over something that cannot be fixed, often something minor. Please calm down, you're just crying over spilt milk. We already submitted the report, so we can't fix it now. A: "Why is Hannah so upset?" B: "Oh, she's just crying over spilt milk. She just fell down and ripped her stockings—she'll be fine."