
I think it's implied he had sex with men before (though also coercive). He can't beat him up, because he's not mafia, he's a politician. If he got arrested for beating him up, to force him to give up his property, the media would have a field day with him and his boss. You can't exactly call the cops on a guy for giving you a blowjob after asking for a blowjob. Also he's currently "pleasing" Pyeonghwa, so asking him for a blowjob would've been pointless. He could've pleased Pyeonghwa by hitting him, but again, that could lead to legal action, which he must desperately avoid.

I think he doesn't want to hit the ml cause he is more gross out by the fact that the ml turns on by being hit and violence is not his thing.
He needs to please the ml but even though he knows the ml is a M, he doesn't really understand the tendency to come up with hitting the throat can make the ml feels good. And he probably doesn't want blow some steam off by someone he doesn't even like because it may switch some weird button in him.
To him, sucking or being sucked, it feels forced both ways so he choose to suck instead. He is tired and kinda submissive in this chapter is one of the reason. His mind went: "I will just do whatever he wants and be done with it. Just go with the flow but not cross my limits too much."
Okay real question now : why would he forces himself to suck him when he can literally beat him up instead? Cause it kinda looks like it’s his first time with a man (I think he’s originally straight or at least it looks like it), and he’s even thinking about his (future ex) girlfriend while looking kinda grossed out. Even if he’s not comfortable about the beating thing, he could also have asked Pyeonghwa to suck him instead ? And I’m pretty sure he would happily obliged like in chapter 10. I mean, nobody is forcing him to suck a guy’s dick, not even Pyeonghwa himself. The dude didn’t even consider it (he was like so down for the beating at first). So why would he goes as far as sucking a guy’s dick ? Even when no one asked him to and he literally has the choice to beat him up instead (or even, just receiving a head while closing his eyes). There’s no way to understand what’s happening in his head. But well, I won’t complain about them FINALLY having sex. I’m just a bit confused.