In a future chapter it is revealed he also turned back in time. After his father’s death, he was emotionally abused by his mother and thought he was following ”righteousness” as his father had. Part of that was putting “righteousness“ above self and family.
Additionally, his family is cursed with huge magical power that turns them into a beast and destroys them from within as they grow older. Thus, his mother makes him believe he needs to produce an heir, and that keeping his distance from his wife is best to avoid emotional pain later on.
This puts him under huge stress, and when she says she would rather die, he offers her the knife thinking she’ll back down. To his shock, she kills herself: the knife is magically imbued to instantly kill whoever it pierces, so she dies at once. He is immediately overcome with regret and begins questioning whether his ”righteousness“ drove her to her death. To make matters wors, it turns out FMC has the power to suppress his magical energy, thus preventing the worst outcome.
As the knife also as time travel power, he decides to use that to turn back time. It requires great sacrifice, and their son decides to sacrifice himself for the magic power necessary in order to make amends to his mother.
With time rewound, ML tries to make amends to her and eventually wins her over.