
Logistically condoms had not been created. You either pulled out or you cleaned it out and either way, they had no knowledge of STDs. So far it seems like Seungho was only sleeping with people who were nobles and let's assume they all only slept with him. Oddly enough I can assume he only has like a 30% chance of getting an std. He's fucked if he gets aids though that's like insta death.

Even if Seungho is promiscuous I doubt we can think of risk as we have today.
If we think of the geography, society and era Joseon period is what? 13XX ? Most STDs of that time were linked to prostitution, location, society. Even if Seungho sleeps with a harem of men, his choices are not that much. We see that they are all the same club of men and let's face it, it's already a push on reality to imagine that openly gay men could be going around having orgies even if they were nobles. Their noble status also probably makes for more selective partners since they don't need to resort to down the street whores who would be serving travelers, etc.
I think that if we think STD, the most probable risks were men like the hobo assassin who truly live on the fringe of society, probably sleeps with a lot of women prostitutes who are just as homeless as he is. And I doubt these people would be sleeping with nobles... I mean Jihwa now may dabble on the pool and then bring the disease to the club. But this is Yaoi after all.
This always in the very back of my mind but does anyone know how exactly they used to, uh, “clean” themselves back there during this time period? Were there even condoms there? Had they been invented yet?... don’t get me wrong, I’m glad they don’t specify, but I’m still curious ( ̄∇ ̄")