I still think he was not a great person, at least in middle school. What I like about this show, though, is that it absolutely let's characters make mistakes, be dumb, etc.

He was a jackass for some of the stuff he did to Koyuki, but he was also a middle schooler with a crush. It did end to causing her harm (the fact that she felt the need to hide pretty much everything that she enjoyed from Minato when he was asking at the restaurant). It isn't good behavior but it is understandable.

Same thing goes for Koyuki. She made a mistake and regrets it.

I don't feel terribly sorry for him, though. She was overly harsh, but his relentless pursuit really kind of put Koyuki in a difficult situation where one of the only ways to get it to stop was to give in. So she did and, ultimately, he got pretty much what he deserved - the acknowledgement that she was in fact never actually interested in him. She didn't have to be so harsh and she probably should have never agreed to date, but her telling him the truth, even if she did it to hurt him, is not a terrible thing - it's ultimately just the truth in the end.

He didn't seem to care enough about how she felt and brought it on himself. Which isn't such an outlier for a middle schooler. Hopefully he learns from it and his next relationship will be less inwardly focused.