A platform goodbye ends at a different moment for the person staying.

Departures are not symmetrical. One person steps onto a train, finds a seat and is immediately busy with the journey, while the other turns round into a station gone quiet and a walk home nobody is sharing. The same goodbye finishes at two different times. That is often why the person staying feels it more sharply and says less about it.

If you are the one leaving, send a message once you are settled rather than hours later. If you are the one staying, put something small in the hour afterwards, even a walk or a coffee. The gap is worth filling deliberately.