It's a prequel and a doujin made by the artist on pixiv. The semes were heartbroken or something bc yuuzen just fucked a woman for the first time so they had sex in the same hotel room yuuzen did just to be able to find some sort of comfort (at least that's what the comments of who read them said). They're both very much in love and obsessed with yuuzen so there's nothing to worry about

So ummm can someone explain why the two semes fucked?