Maybe i'm not thinking deep enough, but it also could be the deeper meaning was just a distraction to a darker plot. His friend says he and the teacher always talk together and she does seem to do a little extra for Fukano, it is possible that she was drugging him to have sex and dementia was a side effect. Before possibly molesting him she says, "forget everything to today as well", makes it seems like she knows something about his ailment. As a result of his resistance she probably stopped her advances and never said anything to reduce the risk of her being discovered.
Maybe i'm not thinking deep enough, but it also could be the deeper meaning was just a distraction to a darker plot. His friend says he and the teacher always talk together and she does seem to do a little extra for Fukano, it is possible that she was drugging him to have sex and dementia was a side effect. Before possibly molesting him she says, "forget everything to today as well", makes it seems like she knows something about his ailment. As a result of his resistance she probably stopped her advances and never said anything to reduce the risk of her being discovered.