I don't think he's a homophobic since Jungwoo did come out to him and his friends before and he didn't get furious or mad. Maybe he likes Jiwon, since there was a scene that was shown on the previous chapter when Jiwon accidentally hugged Seungjin and mistakenly thought that it was Jungwoo he was hugging. Probably Jealousy and not Homophobic.
Also another theory that maybe Seungjin is just upset about them not telling their relationship to him any sooner. Since Seungjin and the guy w black hair(ikyk i forgot his name) are probably the side couple, Seungjin might be just joking or overreacting.
I don't think he's a homophobic since Jungwoo did come out to him and his friends before and he didn't get furious or mad. Maybe he likes Jiwon, since there was a scene that was shown on the previous chapter when Jiwon accidentally hugged Seungjin and mistakenly thought that it was Jungwoo he was hugging. Probably Jealousy and not Homophobic.
Also another theory that maybe Seungjin is just upset about them not telling their relationship to him any sooner. Since Seungjin and the guy w black hair(ikyk i forgot his name) are probably the side couple, Seungjin might be just joking or overreacting.