Looking for specific manga where it starts with the main character being told his wife died.

Then he goes on with his office life like nothing happened, except his eyes start wandering towards a high schooler he keeps seeing on the subway. He becomes obsessed with finding out about the high schooler and it then takes him on a memory trip with him and his wife before they became distant and then he realizes he was following a memory and regrets his actions.

I read it a while ago and it was such a sweet story that it stuck with me.

Thanks in advance!

One of my favourites. It's called Chumo Once Again.