It's definitely the other way around except Seo in doesn't know that Yeongwoon was the victim in his brother's scandal. It's Seo in that feels threatened by Taegu (the gangster guy) because he's managed to help Yeongwoon in ways he that he never could during Yeongwoon's lowest moments. But I don't doubt that Taegu actions now are partly because he's jealous of Seo In's relationship with Yeongwoon since he does have feelings for Yeongwoon. I wouldn't say he feels threatened by Seo in (especially since he couldn't even remember who he was until their second meeting) but he definitely sees Seo in as a parasite in Yeongwoon's life since he and his family are a main source of trauma for Yeongwoon.
well i agree with you about seo-in he's obviously very threatened and jealous as he shows it with his words and actions so i didn't need to mention that. i was trying to understand taegu's intentions better but your take about him makes more sense than mine tbh
i feel like the gangster guy now wanting to take stand for yeongwoon and take revenge for him after 10 years is just bcus he has developed feelings for him and is lowkey threatened by seo-in and is competing with him bcus he wants to prove he's better than him and wants yw to choose him over seo-in (just my opinion tho)