spoilers:
ml becomes an extreme green flag when he realizes his feelings for mc. this is a novel about regret/grovel/tragedy. ml falls in love with mc, whom he used/abused, for basically no reason at all, and that becomes his karma and weakness. admittedly, the change is very jarring bc of the vast difference between his past self and future self; but soon after he realizes his feelings an incident happens (which is entirely his fault) then there is a 5 year time skip where mc pretends he is dead and ml is consumed with regret/despair to the point he tries to commit suicide, so with that in mind, the 180 personality change (only with mc) that partly came with elation upon discovering mc was alive kinda makes sense. that aside, imo the redemption is pretty good. ofc, the fact that mc never forgives him 90% of the story, and other characters and even the narrative itself never let ml forget what a scumbag he was is doing the heavy lifting. but the story ensures ml suffers the consequences of his past actions, and reminds him that it is his karma, and as a result, he becomes a groveling simp who would do literally anything to earn his forgiveness. he would lap up any scrap of attention mc would give him, even knowing it's false. he doesnt give a crap when mc tries to kill him multiple times. he would even voluntarily die if that's what mc wants, which finally moves mc. at the very last chapter, ml lets mc go and says mc can return when he has fully forgiven him and can move on from the past, which only occurs after 6 years. ngl i quite enjoy angst novels with groveling mls, but im pretty picky... but this story was really satisfying and cathartic.

How does a man so cruel, suddenly has his concious awakened that he repents the things he did. I don't believe for a second in this redemption arc.