If Ji-tae was going to stay off his rocker for the rest of the story, his mental break would have been framed in a positive light. A wake-up call to the cruel realities of the world, or a determined vow to Become Strong No Matter What Evils I Must Commit. (That’s how the traditional edgelord characters begin.)
Which is not what happened; it’s framed as a horrifying, desperate way to cope with the realization that Maria is just using him. He’s making all these creepy, contorted faces designed to unnerve the reader. It’s not “positive growth” within the narrative, so unless the story is supposed to be a slow decline into madness/messing up your life and end on a low note, he’s going to recover somehow and grow from it. (In the case of edgelord characters, their decline is “positive growth” in the eyes of the narrative, so they never snap out of their bullshit.)