god is good just now that helloooooo
I would say the author uses irony in this passage that remembering his mother makes him not happy but miserable which may be the opposite of what is expected but he would rather suffer this than be happy in forgetting her as this latter feeling would be expected to make him sad.
I would say that the best theme to address those key points listed, would be: A. Feeling hopeless is unreasonable when faced with challenges. In other words, we shouldn't feel as if the end of that world is at hand, just because challenges and tests come our way. That is to be expected. Hope that helps.