Koisuru Milk Crown @ Onsen Ryokou

Sakisaka Reon, who works at a boys' bar, is in a steady relationship with cafe owner Hodaka Shuusuke. Spoiled by his older boyfriend and constantly having new sides of himself drawn out, Reon finds himself both flustered and comforted by their relationship. Then one day, Reon, along with his coworker Kazushi and Kazushi’s boyfriend Ao, sets off on a hot spring trip with the four of them together...

(Source: Ichijinsha, translated)