It's probably a hallucination and not an actual ghost, so she will go away when he starts feel better.
She isn't the problem, just like the anonymous said, it's more like an hallucination because he still didn't get over her. That's why when he is with Jimin she disappears.
But in the more recent chapters she appears to be more like a ghost rather than a hallucination since she's now affecting Jimin as well (such as when they were at the motel and Jimin overlapped with her or at karaoke when Jimin said that it felt as if he was possessed)
Can the ghost girl just go the fuck away? Like it's not that I hate her because she's ruining any ship. I hate her because she's ruining the protagonist's sanity if she had just went away this story could have gone by smother because the protagonist wouldn't have been as broken. I'm not saying the author should remove her because the whole element of the ghost makes the story so unique and thought consuming but SHE'S GETTING ON MY NERVES! I love the mc and she's just breaking him apart from having a normal life, not letting him move on.