Greetings, friend @fitinfun.

The nests are not eternal. We can see the birds, they use their nests and then abandon them. Then we found empty nests in the trees.

Seeing an abandoned nest will always be a sad scene.
But the children will grow and leave. Forever.

The ones staring at their kids no longer live in sometimes get really sad. The ones that left sometimes wish they could see their kids more often

In both cases you will always feel sad. But life goes on.
In fact, all this is part of life itself.

All best, Piotr.