because you could always just pick up the book / rewatch the movie/TV show / re-consume the media again but it’s not quite the same. it’s not just “I miss discovering everything new about them” but also “I miss who I was when they filled my waking hours.” yes we joke about a character/book/movie/TV show living in our head rent-free but when they move out, you feel their absence. they haunt you, or perhaps, you haunt yourself with the memory of what it had been like, because there’s the bittersweet knowledge that you have also changed since you came into contact with this text or this character, that they have changed you with the revelation of some experience or identification or emotional truth, and you now carry them with you wherever you go but you will never be able to fall in love with them again for the first time