Aimai Na Kankei曖昧な関係; It has become natural for us to be together

From 'Mijuku na Kareshi' Summary (by torrentchan): Yet another great oneshot from the infamous Masara Minase! This oneshot is about Satoru, a single bussiness man whom had lived alone since high school. One rainy night, Satoru picked up a high school male stranger and give him shelter. Little does Satoru knows that this high school boy might be his dreamfilled escapade. After all... Note: There is also a follow up oneshot called 'Yasashiku Toraete (Capture Gently) According to MyAnimeList, this is part of a collection of one shots. The order goes like this: 1) Aimai na Kankei 2) Yasashiku Toraete; sequel to (1) 3) Itsuwari no Daishou (False Compensation) 4) Man On! 5) Kodomo Ijou Otona Miman 6) Sweet Restraint; (Amai Kousoku) 7) Miracles Don't Happen (Kiseki wa Okorenai) 8) Mijuku na Kareshi; extra to (7); (Childish Feelings; Immature Feelings)