In terms of his feelings: This is the first time he’s seen Maria murder someone (well he didn’t see it but it happened in front of him) , he’s finally seen just how far she’ll go. That’s scary for him.
He blames himself for everything because Maria had to save him and he couldn’t do it alone.
He blames himself for the death of young woong because if he was just able to defeat young woong then Maria wouldn’t have had to kill him.
And now he doesn’t know what’s going on.
He’s confused, he’s scared of Maria but he’s also feels hugely guilty. So he’s talking about how dangerous maria is because he’s subconsciously scared of her but he’s also apologising because he feels like once again, his lack of competence has resulted in bad things happening. He feels it’s his fault. Therefore, he feels so bad about himself that he’s genuinely sorry for being born. He’s not just a mad man.....he’s traumatised, depressed and in pain.