water under the bridge
過ぎてしまった事、取り返しのつかない過去
Ex
- That’s all water under the bridge.
- It’s water under the bridge. You have to move forward.
Reference source
- https://ejje.weblio.jp/content/water+under+the+bridge
- http://www.beo.co.jp/atoz/english/water-under-the-bridge.html