The musical was written to show what Phangirls are missingThe musical was actually designed to show why the Phantom and Christine can't be together and why it would be disastrous, and that the only way they would be together is if everyone was derailed and way out of character.
This was written to spite phangirls and Sarah BrightmanAndrew Lloyd Webber was bitter about his divorce and was tired of all the fan mail and complaints on why Erik and Christine can't be together that he found a novel where Christine died and turned it into the musical for his own satisfaction.
This is all happening in the phantom's headYou know how everyone seems to think that Christine dumped the phantom because he was deformed and not because he was crazy? Well, in the first musical, the only character who actually seems to think that is, wait for it... the phantom. Also, he's rich, successful, everyone loves him, except for Raoul who is inexplicacly terrible because he hates Raoul. The reason Christine dies is because he's more aware of her not being real than the others, so his mind writes her out