I'm sorry that memories make you sad but I know too well how you feel.
My baby is all grown up too but he is the reason I am and I realize that they never stop needing us, if only just to be.
We as parents are always needed though maybe not always shown, but needed by our children in the sense that they know we are here for them if they need us.
We can always make more magical times to remember even though time has passed and things aren't the same, but we can make these days magical memories too.
I hope that you can feel happier.