Being emotionally compromised causes people to make decisions that don't make sense.
I'm in no way defending her but her feelings of insecurity, jealousy, and inferiority overtook her feelings of love for the MC which made her emotionally connect with the other guy.
Now she has to live with the fact that she emotionally destroyed the one she actually loved and has to live with it.
Due to the time skip we don't exactly know how that has been for her but we see it in the MC - he is broken and aiming for a goal that doesn't exist.
The last page you can infer what she is feeling and it would be safe to say she is not just feeling one specific emotion when they made eye contact.
Like I told the other guy, I’m sorry if this has turned into a never-ending cycle of disagreement—that wasn’t my intention. So, I’ll leave it at this: you’re basing her reaction on his emotions, saying she feels guilty because you believe she thinks she broke him. In my opinion, that’s an improper way of looking at things.
While he was elevating himself, she never thought about him in that light. When she had sex with the other guy, she wasn’t thinking about his feelings in that light either. The panel takes place years later, and what’s happening now? He’s getting promoted. And she’s ashamed to look at him. She sees him standing there, accepting the promotion, but in that moment, there’s no way she’s thinking, Oh, I broke him. That’s illogical. Women don’t think like that.
Is there a chance she feels guilty? Sure, but I doubt it. Her actions throughout the chapter have been driven by jealousy, and I believe this moment is no different. He’s now the head chief—he’s surpassed her. She was his senpai, but now he’s the top dog. And the whole time, she’s been jealous of his success. Why would this moment be any different?
Basing her actions on how he feels just doesn’t seem right. It’s an improbable way of looking at things because she couldn’t possibly know how he feels. Could she think, I must’ve done something to him? Sure. But clearly, she’s not.
Let’s just agree to disagree. I’m sorry for dragging this out as long as I did—that wasn’t my intention. I respect your opinions, yours and the others’, but that’s just where I stand.