我和他有一个难受的前关系。

好像也可以形容事情变化的很快，就像流水一样快。

桥下有溪水

We say "water under the bridge" to refer to past experiences and conflicts which we have decided to forget. This idiom compares these memories of the past to water which has passed under [the] bridge. Example: "Aren't you still angry about what he said?" Answer: "No, that was a long time ago. It's all water under the bridge."


source: http://www.goenglish.com/WaterUnderTheBridge.asp