I can't agree here. It's your decision to forgive or not forgive somebody. If you feel that the reasons to forgive is not enough or you just doesn't have such reasons, then what? Tbh, he forgive her anyway, but the "distance" between them is different after this choice.
In short, I completely disagree with the position that you can only be mad at someone who meant something to you, while everyone else become forgiven by default, because they mean little to you. It all depends on the person's act, your vision of the situation and possible explanations and motivation of who you plan to forgive or not.
Even the game strongly hints with the consequences of this choice. That if he is mad at her, then he is quite cold with her, even rude in places, and the best option in this case is if they can restore friendship, but without something more. While forgiveness allows you to slip through a significant stage of gradual reconciliation and, perhaps, return to something more besides friendship. But for some reason it looks like that you see this situation in inverted way.