Speculations..

He looks exactly like his mother from the flashbacks on the previous chapters. How did u even come up with that. ┑(￣Д ￣)┍

It's a speculation. What other potential reason can you think of that makes sense?

obviously because his father was having a hard time trying to cope with his own pain caused by his wife's death :/
and his son resembled his dead wife a lot, so ofc it was hard for the father to even look at his son's face?? because every time he looked at the son he saw his dead wife?? but he still tried to provide haon with everything he needed(teachers, clothes etc.) except for the emotional needs, bc the father himself was dealing with his own sorrow and loneliness after losing his precious one.
the way the person reacts to the trauma and copes with it is different for everyone. and the wife's death was obviously a traumatic event for the father, and his way to cope with it was to distance himself from everyone, especially haon, whose mere was reminding the father of his loss. so he neglected his own son, which is definitely inappropriate behavior. he had a reason for such a behavior(his trauma's consequences), however, it's not justifying the behavior itself, of course.

I understand all this, it's obvious from the story. But the last chapter just seemed strange to me. Haon was thinking most of what you've said, but his father didn't confirm it. He made a face as if there was another deeper reason. Hence my speculation... about if there's more to the story than the most obvious conclusion.