Word. The story is already the right amount of trope. Please author save us from the Oprah version of 'everyone gets a car' where every man in the story gets paired with a gay lover.
That being said, that's Yaoi for you. A male character makes one single appearance that is not even remotely romantic and our fujoshi mind already come up with ten theories of shipping... Seungwon was supposed to steal Nakyum's heart or seduce Inhun... now the assassin apparently is supposed to kidnap Nakyum and make him fell in love with him, if he doesn't bed Jihwa first, lol.
About the drawing, it seems every artist has the same behavior... just like when you are reading a story and you recognize the author by the seme or uke. The new guy looks indeed like Seungho's homeless brother with slight rounder lines.
Every single character in is hot in this story and when Seungwon showed up it was all the rage... so maybe that's why the new guy just looks average now, lol. He even looks like a rough up Seungho.
I may be against the flow but I do hope this is not every male character that shows up turns gay. I hope the assassin just do his thing and gets killed because if he tries to kill Nakyum, that's what he's gonna get.