I will say that he got too one-track minded regarding his goal but that doesn't excuse or justify anything the girl decided to do. Also, she clearly has some form of regret/guilt if we go by the last page but that's honestly not good enough.
Honestly, I don’t understand why anyone thinks she felt guilty in that last panel. If she truly felt guilt, she wouldn’t have gone through with having sex with his rival while he was standing right there in the doorway. She looked, saw it was him, and still made the conscious choice to keep going—no apology, no pushing the rival off, no attempt to explain, and no acknowledgment that it was a mistake. She just continued.
The real reason she turned away in that final panel isn’t guilt; it’s because he was being promoted to editor-in-chief. She’s jealous of his success, just like she’s been throughout most of the chapter. A person like that isn’t just insecure; she’s diabolical. She’s preying on his downfall because she can’t stand seeing him rise above her. She set the conditions for him to meet her expectations, and he did. But now that he’s excelling and moving up in the company while she’s stagnant, she can’t handle it.
He’s working hard, believing he’s proving himself worthy of her, but the truth is, he deserves better. She knows she’s a horrible person, and her actions make that crystal clear. I don’t believe for a second that she felt any guilt. Everything about her screams jealousy—she’s been acting that way the entire time.
In my opinion, this writer has created a despicable character, plain and simple. That’s all I have to say.