An Innocent Puppy Meets a Two-Faced Cat (2015)

Blurb:
A mild-mannered gentleman, good at his job, and reliable; Naohito’s been wearing his mask of “perfection” for so long it’s become as easy as breathing. That is, until he meets HIM. At the behest of a childhood friend, Naohito grudgingly attends a singles party for twenty- and thirty-somethings. With zero interest in mingling with the crowd, Naohito sits off on his own—and meets a much younger man, Tohru Akasaka, who clings to him like a puppy. Naohito’s barely able to cope with Tohru’s youthful energy, and they go their separate ways … but in a twist of fate, end up meeting again. Naohito’s life is flipped upside down by his companion. Will he give into this young man and let his mask drop!? Find out in this heart-pounding tale of two lovers as they struggle to overcome their age gap and the trials of living under the same roof.

Source: www.anisearch.com/manga/26457