Ok, been a few years since I read this but here are the details I recall:
A wedding or something of the like happens, and after the guy gets back to his apartment a girl from the wedding enters from the window and they end up having sex.
Many volumes later in the final chapter...

There is a 10 year after, he ends up working in a lighthouse and she married another guy (why they went their separate ways). He just died, and she introduces the original guys kid.

Does anyone know the name?

Asatte Dance for sure. 🙂