People make mistakes all the time, as a girl, I hurt my exes unintentionally before. I don't think there is anyone who are free of guilt, never hurt a single soul ever in their life. If someone believes so, it's just they weren't aware of their own actions. If the ML put into effort and try to redeem himself, I think it's fine to forgive him, since forgiveness is a good virtue to have. Our modern society is full of people who always try to judge others so hard. One red flag and you're the unforgivable scum who deserve to never be happy again. This cancel culture is quite toxic, it also promotes the idea that people are replaceable, one mistake and you will get discarded, because there are plenty of fishes in the sea. It's sad to see this in the comment section here, as I believe the whole point of this story is about forgiveness and redemption. That's why there isn't a second male lead yet, the author really wants a redemption arc from our MLS.
wait - what about this story makes you think that "forgiveness and redemption" are the key themes?
I see them as "empowerment and agency", if anything.
Since the start, Nicole has only shown actual emotion and happiness, or a sense of fulfillment, when she was
not dealing with Keios, and was instead pursuing whatever she thought interesting or promised opportunity for herself, but in the short-term and the long.
Keios hasn't made "a mistake", or even "several mistakes" here. He spent literal years completely ignoring his fiance for another woman, and has
only "come around" to his bullheadedness upon realizing that his future marriage was in jeopardy due to who and how he is as a person, and
that was only after he had to be repeated smacked upside the head, figuratively and literally, by both his peers and his parents.
Even now, he can't bridge the gap and treat Nicole as a person, and is instead
still only thinking about himself and their marriage as it pertains to his own situation and convenience, while
currently thinking himself superior to another man whose behavior reflects a Keios from not nearly long enough ago.
Forgiveness is all well and good, but it has to be earned, and Keios has come nowhere near close to that mark.
Simply going "oh Nicole should forgive Keios and all the readers condemning him are being toxic" is ignoring everything the plot has shown us up to this point, simply to accommodate your own views.