
I want a good ending for koichi also. Because he really put effort into his relationship even though it was too late, I still acknowledge what he did.
No matter what the reason, hurting your partner is wrong and is also a crime. There is no scenario where that is okay. But even though he gave into that violence for a while, he regained his sanity and let his lover go.
I'm sure the pain that he will go through for hurting his lover is not gonna be easy to get over. He also lost the man he loved due his ignorance. He will be very much n love with mitsuru for quite a long while before finding someone else.

That's exactly hat he's experiencing now. The person he loves has left and no matter what he does he can never be loved by the person he loves. He's been abandoned that's a pain that will be hard to overcome as person. I think he has paid in full for both his ignorance and his abuse towards the man he loves. So I have forgiven him and wish him well.(〜 ̄△ ̄)〜
This may sound evil but I don't want Kouichi to have a happy ending( ̄へ ̄)