
Here's the thing. Maybe I'm reading too much into it and seeing more than there is to see or intended to be perceived.
But nevertheless here's my opinion about this last story, also drizzling a little of what I feel abou the others:
There's obviously no hero here. No likable main character. You're not supposed to root for them. They are both not very healthy people, both with some deep rooted mental issue. His is rooted in trauma whilst her's is hard to tell since we don't know much about her past and childhood. They both to some extent think poorly about themselves, which is why they allowed themselves to reach this point.
He thinks is love, but from we can analyze based on his actions and words, it's just an obsession, admiration. He first got interested for her for something as simple as her perfume. Something that easily could've been used by someone else, it could've literally been someone else if not her. Then he found her beautiful. Her distant demeanor whilst also seemingly slightly interested in him made him feel hopeful and he liked the thought of having someone he admires being interested in him, even if very so slightly. He took all the crumbles she gave him happily, eagerly waiting like a dog even though he knew nothing about her other than things everyone else who works at the company also knows. He created this image of her and put her on a pedestal. Romanticizing their situation even though it's an affair. He doesn't ask her deep questions, he doesn't try to hard to think about how she feels with all of this and also, he is delusional enough to think anything good could come out of someone who's cheating on her fiancee. He accepts all of this because he thinks that's the best he can get, and also because he hopes of a fairy tail of overcoming all of his past and in the end having a perfect life with patience and hard work. These affirmations he has on his fridge show how much he tries to keep himself grounded, but he's young after all and he can't help it.
Now onto her. She is even more self-destructive. She believes she is broken, evil and disgusting. She thinks she doesn't deserve good things and overthinks everything in an attempt to racionalize her situation, feelings and therefore, her behavior. She tries hard to tell herself that everyone is like her, sometimes worse, and so there's no point in sulking or dwelling on it. It's uncomfortable for her to think otherwise, specially when she believes that she feels joy in hurting good. Contradicting in fact, her second most big affirmation: people are fake. This self loathing only grows because she is in a loop she put herself in, unhappy as she keeps herself where she believes she deserves to be, with someone "just like her". A "mirror". A reminder. A checker. To regulate herself into not forgetting her "place". But she never once tries to wonder where this comes from, why does she believe those things and why does it allegedly bring her joy? Because she thinks the ml is good, but she feels horrible/guilty for doing this to him, which debunks her main affirmation. And she can't help it because she likes how he makes her feel. He brings her out of the box she put herself in.