Sorry late to respond but no I'm not talking about the chapter posted here cuz it's incomplete...I'm talking about the chapter I've seen in raws (i didn't buy the manga but usually if you look up for a Japanese manga u can veiw the first chapter for free) it seems like there's two volumes, spoilers below:
So right when it was cut on the first chapter here I guess we can already tell but the one who came behind the doc (uke) was seme's brother in law- n.b. I don't understand Japanese but I used the translation to some part of the chapter I screenshoted- anyways right the he was talking with the uke and their relationship seems suspicious as he told him that they could go relax together in bed and hugged him from behind and while touching his waist with hand he kept releasing his pheromones while whispering in uke ears but seconds later the uke told him he's busy and got away then the said bil reminded him of his appointment with the seme the after that scene you see the doc rush to the toilet to masturbate and release hiss load that's what happened........also there's the fact that the second volume poster had the uke in between the seme and seme's bil so it's for sure pointing to something
I just feel bad for the seme he seemed really naive and pure in his interaction with the uke in the rest of the chap and knowing that his bil is two really adds up to how shitty the situation is gonna be for him(〜 ̄△ ̄)〜
Just got to see the first chapter and that brother in law is a cheater