Because he finally got his revenge lol I doubt it’s just about Sihyeon
He hates Gyu hwae to his core but it's clear from the earlier few panels that the liquid covering Sihyeon's inner thighs is what pushes him over the edge. But then again the author did stresses on how Seungtae will become an overly maniacal possessive bitch down the road. Perhaps that road isn't closer than expected.
stressed*
Is* wth...
Off topic but I hate misspelling words too it bugs me when I post comments and that shit is missing things lol
But I agree I think it’s mainly “how dare the man I need to have revenge take my boytoy who I want to ruin affectionately” xD
Y is he that furious now? Last time i checked he was whoring out Sihyeon to an old man.