Actually at the last regression, it was actually jihee himself that turned back time in order to meet mc again, you can see it from a previous chapter that he used a time regression skill
That's what he always did—on his own. And according to the plot, he was really tired of it. And MC promised him that that was it, he didn't have to come back anymore. That's why the ending pissed me off so much. He's back again. Only the person he had a relationship with is gone—he died along with his memories. And Jihee will have to go on that raid again. And if MC dies again, he'll have to go back again. And so on, in a circle.
Have you read the novel? Does Seonwoo get his memories back?
I'm SO FUCKING angry. The main idea, the main promise, was that Jihee wouldn't have to regress anymore! Instead, he's just stuck in this damn Limbo. It's monstrous.