https://booktoki330.com/novel/4995951?stx=무흔의+밤
There is no English translation yet so I used MTL. It was worth it tbh, they are really cute.
There isn’t but if we want to be picky, blondie kinda is. Gwangsik (the blond exorcist) develop a cute crush on Seungju toward the end but it never cause any problems for MC and ML (Muheon just get jealous sometimes but in a cute and fluffy way). And Seungju never ever started to acknowledge him anyway.
Blonde guy name is Yeonho (nicknamed Gwangsik). He is part of the secret team 0 where Muheon is the team leader. This team is only know to the executives and is charged of different investigations and stuffs for the exorcist association. This team is also only composed of orphans snatched by the association and are trained since young to be basically perfect little soldiers, with no emotions (that’s why blondie lack emotional sense). Most of the members are between 16 and 20 years old (it’s illegal for the association btw, as they need to be adult to work in this field) and don’t have a real identity (no real name and no real birthday).
Blondie is 18 years old btw (16 years old if we consider international age).
Muheon basically accepted this position because it give him lot of right and the possibility to disband this team (which is one of his main goal) and treat these child better.

Slight spoiler from the Novel about the drunken sex because I know it can bother some people.
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Y’all don’t worry ML is a green flag. He didn’t have sex with the MC, just helped relieve him with his hand. If the MC had muscles pain it’s because he slept in a wrong position lmao. As for the scratches on ML’ back, it’s because Seungju has the bad drunk habit to -literally- climb on people and kiss them. If Muheon didn’t clarify things, it’s because he thinks SeungJu has that drunk habit with anyone and he was getting jealous lol. So he let our MC think they had sex so that Seungju feel conscious of his habits and won’t go and drink till he blackout again.
When they have real sex for the first time, Muheon tease Seungju about that and said « If we had sex back then, you wouldn’t had been able to get up the next day »