I don't know but if it was me i'd also forgive the guy. I mean yeah what he did what fcking wrong, having sex with someone else, cheating. But... I think he was just... confused, like he's searching for something he never felt before. He never experienced love at all, i pity him for that. I hope, soon, he'll realize that he loves sachan (i also hope Sachan won't break up with with him)
Dear Sa-chan