Here we go: Ootsuki Mio's "Tonari Ni Kimi No Nukumori Wo" released over a decade ago: http://www.mangago.zone/read-manga/tonari_ni_kimi_no_nukumori_wo/mf/v01/c001/
Or maybe they didn't know? Let's be honest, yaoi tropes are extremely limited.... I doubt that publishers/editors would knowingly allow plagiarism. Or maybe the two authors are friends and this is a remade version of the other one, with permission. who knows.
Without bothering to credit the original author? No offense, but that sounds like grasping at straws. This is not a typical trope story. The present one copies Ootsuki Mio's plot-point per plot-point. It seems to me that Yamamoto Aturu thought that, after a few years, nobody would notice ...
For Pete's sake! I just read another manga, not too long ago, that is almost an exact copy of this story. Boy loves dog. Boy has no other life. Boy loses dog ... and the rest, too, almost word for word.
I don't know which story was written first, but someone certainly plagiarized the other.