@Enok I think it's more that Hayeon feels like she isn't needed anymore, which feeds into her already low self-worth and confidence issues. The first chapter showed how lonely she is and Hayeon told Minwook she never had friends because she moved around a lot. Woojoon is her first real friend and she felt responsible for his well-being. Without her looking after him at the beginning, he would've been all alone like her. She felt that Woojoon needed her which is why she ended up doing so many things outside of her comfort zone, like hanging out with strangers and sticking around at first even when Joohee hated her guts. But seeing Woojoon adapt to Hyunsoo's surroundings and grow more independent so quickly shows that he doesn't need Hayeon as much as she thought. She's back to feeling lonely because she feels unneeded again.
I mean, look at how she is with Minwook. Her interactions with him are very telling of her personality and struggles. Her low self-worth and shyness are on full display there. At work, she doesn't even think to ask Minwook for help when she runs into a problem and always tries to solve the issues on her own even when he told her he's there to help; or when he gives her a genuine compliment, she feels the immediate pressure to live up to his positive impression of her (not wanting to fall asleep in the library and disappoint him). And then look at how she reacts when Minwook tries to cheer her up: she thinks "Minwook is a good person" who's nice to
everyone, including her. It's like she believes if he's nice to her, he must be nice to everybody. The fact that he kinda has a crush on her doesn't even register in her brain because she's basically been ignored her whole life.
As for Hyunsoo, I don't know what she could do at this point to try and bring him back, especially when Woojoon says he had no idea how he ended up in his body.