Oh he's beyond insecure cuz he just clearly told him "Just swear you'll tell me next time when something come up" and before that he made it clear he wanted in on matters related to yeonwoo. He questioned why he always goes to that thug instead which translates to "I don't like it, depend on me not him". Now obviously yeonwoo didn't catch any of that despite it being said and just responded with hesitant "yea okay"
Now after that conversation by a day- he sees him in the thugs car lol. The same guy who told him he has no right to be by yeonwoo keke. At this point, he can't get away with being ambiguous he has to spell it out to yeonwoo otherwise I'm scared seoin will murder the thug
so true the messages were sent but not received lmao! but like itd be nice if he'd let yeonwoo have other close relationships especially cause thats part of who yeonwoo is, he's a friendly guy. but i think seoin's anxiety and fear of abandonment require a lot of attention for him to get to that level of healthy... (also - i think of the thug as a father figure to yeonwoo not a romantic partner cause otherwise its a lil groomercore)
let the man decide if he's gonna watch his father die or not in peace! not everything is about you seoin even if you love him and you're the prettiest man ever seen! privacy is important when building trust he would've told ya in his own time!