
Yeah, because he's in such a clear state of mind right now, that he will just stop and think lol
Nope
He saw it, but he's in denial. He denies and blocks everything that contradicts his belief of being abandoned by Nakyum. And he's hurt, angry and completely lost in rage. There's no reasoning with the person in such a state. He needs to snap out and only then facts will be able to get to him.

Exactly. And that bruise hasn't been shown to us before either, it's the first time we see it too. Drawing takes time. The author wouldn't be drawing unnecessary scenes that don't add anything to the plot.
I have a feeling the doctor might be summoned to examin Nakyums hands and this could potentially reveal the second bruise, on another wrist. Now, that will be hard to explain.
Because right now the first bruise the we saw, and Seungho saw, could be perceived as the bruise that Dokje caused. And perhaps that's why Seungho hasn't immediately stopped to check it out.
But if the second bruise gets revealed on another wrist? Then that will be hard to ignore and it will be evidence that something's up.
speaking of ch. 63, in one of the panels, do you guys think seungho was staring at the bruise on nakyum's wrist from being tied up? i wonder is he's finally noticing smth is off