How to define this...

It's so easy to get emotional and all sentimental.

I was standing on the empty crossroads, listening to the rustle of the old peepul tree, watching my son throw stones at the calm evening river. Part of me was lost in the beauty of the moment,
awe-struck into silence. And the other part was recalling many incidents over the years of my childhood, which were related to this place, to this peepul tree, to the evening breeze of this river. I wanted to pull back those moments from the past and relive them!

And there was this grief that those moments and those people had just passed and faded away, out of reach and gone forever.

There were many places that kindled this joyful grief. I was visiting my native village after nearly a decade. The village hadn't changed much, apart from a few things here and there. Kids had become adults, adults had grown old and fragile and the old had departed. The Sea still roared with a silent majesty. The river flowed effortlessly into the vast blue. Familiar faces smiled back on the roads with 'how're you?' It was like I'd visited it only last month.

Yet there I was, trying to hold on to the memories these places evoked in me. Fighting an invisible pain. Not knowing how to heal this wound. Not even knowing why this wound exists in the first place.

No, it's got nothing to do with 'stay in the present, let go of the past' thing. This emotion beats my understanding. It's not grief... grief or sorrow is not the right word.

It's something subtler.

update: the answer seems to be Mono no aware(the pathos of things)

it's a japanese term which describes the awareness of the transience of things, along with a gentle sadness at their passing.