I honestly don’t blame Iwanako that much. It’s not like she stopped visiting because he was disabled. It sounds like he made no real attempt and just kind of sat there in the sorrow he felt.
I don’t blame Hisao much either though, he had just gotten tough news that was hard to deal with. But I don’t think it’s entirely on Iwanako.
In another world where he decided to make the most of things, maybe him and Iwanako could have still been friends, and even still dated.
But it feels like part of it is based on it not feeling right to be around him when he was like that, which caused them to drift apart.