Please help!!

Hi, anyone knows the title of this yaoi manga about 2 salary men who are office colleagues. They are the 2nd couple (the main character is also their colleague). One is a playboy and the other is somehow ignorant of the adult world. They are both hetero. And not really on good terms but they are not enemies. But one night, the playboy and him went on a goukon with old or not pretty ladies (?). Then the playboy wants to escape so he told them that they are a couple and kissed the innocent boy. After that, they went to a motel to just rest. But then the playboy wants to try to have sex w/a guy then they tried it. From then on, he cannot get his dick up with a girl and only with the innocent boy. If I remember correctly, the title starts with letter S. Thank you so much in advance!!