What are the sentences about "the old don't go, the new don't come"?

There is a saying: the old don't go, the new don't come. For feelings, it's not like this. Sometimes old feelings can't be let go, and new feelings come again.

The back wave of the Yangtze River pushes the front wave, and the front wave dies on the beach.

survival of the fittest

Some losses are doomed, and some predestinations will never bear fruit. Love a person, you don't necessarily have it. If you have someone, you must love her well. ...

Don't be too sad. The old ones don't go, and the new ones don't come. I'll buy another one when you behave well.