This last section of story is missing some plot explanation. It was hard to determine what Shingo and Keiichi were fighting about (lack of communication?). The story feels rushed in sense that there was a lot of build up to their separation, but the resolution was simplistic. Actually, I've gotten so that I'd like to see more of Older-bro's life with his lover, and son Rio.
Kuroneko Kareshi no Afurekata