Hmm where are the parents/teachers/any adult in this situation? I think writing for someone to kill themselves on table would warrant severe consequences? If you are going to make a "drama" one-shot at least make it somewhat believable holy lmao
Believe it or not, this kind of situation does exist in real life. It's called "Escapism" where your mind refuses to accept reality and believe the imaginary stuff in your head as the real 'reality.' It's not about seeking helps from parents or teachers, but it's more about accepting reality in one's self. In this story, for example, she's all alone with no friends or adult figures to talk about because she doesn't feel like she needs to--she got herself an imaginary girlfriend to talk with, after all. And even if she's talking about the issue with other people, it may work against her instead. More people might think of her as weird, she'd become depressed, and in turn becomes even more indulged into her own escapism.
As for escapism itself, humans have always found themselves in this kind of situation and tried to shun away the reality with anything that they see as the ideal 'reality.' Talking to an imaginary person, creating a make-believe life story inside their own head, indulging themselves in the reality of a certain story and thinking they're a part of it, the list goes on. This is why the only way out of it is to accept the reality, and the escapists themselves are the only ones who can do it. Other people who are truly supportive of them (and they're very, very rare) can only remind the escapists of the reality and not more, otherwise misunderstandings may occur and things could go downhill.
This is from someone speaking through experience as well. It happened to me, this whole story. Amidst my depression, I just found out that I'm actually gay and interested in one of my best friends. But I knew it would be impossible to be with him because other people (including him) would think of me as weird and dangerous. I feared my depression would've gone worse and led me to suicide, so I just imagined myself having him with me, thought that maybe I could get through my harsh situation. But the more I lived with it, the more it hurt every time I met the real deal. I didn't want him to hate me, we've been friends for years and he's always depended on me. Because of the consequences, I just thought that talking about it with other people would be meaningless, and I could never find the right place and time to talk about everything. So I ended up crying by myself every day, which is again another form of my escapism.
So yeah, this story is just as real as life itself. The problem isn't as simple as "Find adult figures to sort things out," it's more about accepting the reality. She has accepted the reality through more bullying, which is a slap to her sense of reality. Thus, her "Yuka" is finally gone from her mind.