forgot the name of the manga but basically the mc is an author i think and he travels somewhere and stays at a guesthouse every now and then and its hosted by a brother and sister and the brother (the ml) plays piano..? the sister is ill and eventually passes away. The mc and ml separate for a bit before reuniting. The mc was also engaged to someone else but gets a divorce later on.
Might be this one?
https://www.mangago.me/read-manga/bright_blue_ni_shizumu/
crying theyre just so fucking lovely. Literally soulmates.