The meter is wrong, because it is a limerick, so I will avoid talking about it for now, but limericks also need to have rhymes, right? The fourth sentence does not rhyme.
In terms of words, the old friend returns, does it mean that the old friend has returned to his hometown? Come back to your place? Because I don’t know what situation you want to express, if your hometown is the same as yours, you can leave and go back. It can also be consumed now, without any shadow. Tingfeng suggested using the moon watch.
My personal abrupt change is as follows:
The cherry blossoms bloom and then fade,
An old friend left but did not return.
Looking through the autumn water without a single shadow,
I lean on the railing alone on the cold terrace.