It would be the best for Rei to stop thinking about Kyoko and Gotou at all. View them like they were strangers who have got little to do with him. The more he keeps them in his mind, the more negatively emotional he becomes, yet he still can't do anything about it. At the end of the day, Gotou and Kyoko are adults, so who is Rei to tell them what they should do? Above all, getting involved undermines his attempt to keep his distance to the adoptive family. Of course leaving them didn't exactly fix anything at all, but at least it did prove Rei is a man who walks the walk, not only talks the talk. Too bad Kyoko is too bitter, wrathful, and self-destructive to actually understand it. But that's her problem, not his. Rei did what he could. Trying to do what he can't won't help anyone. The sooner he realises that, the better. He should spend that brain energy instead to train his shogi skills.