I must've been in a mood the first time I read this, because on re-read, this is just LOVELY. It's a quiet established relationship that endures long work hours and eventually a long-distance relationship, but their bond is strong and unwavering. I also love that the MC's parents adore his boyfriend (though I am not sure they realize they're dating).
ETA: On third read, I've decided the parents must know. The boys live together in Japan and the US, they have Kazushi's parents over for dinner in their apartment where they share a room (and the boyfriend cooks), Harutomo calls Kazushi's dad "dad" which seems awfully familiar? (we only do that here with in-laws; maybe I am projecting), and they joke about adopting Harutomo into the family. Also, Harutomo texts photos to Kazushi's parents. It all seems quite intimate, so I like to imagine they're very aware of the relationship!
Aishiteru (FUJITANI Youko)